Air Force Institute of Technology Research Report 1997

This report summarizes the research activities of the Air Force Institute of Technology\u27s Graduate School of Engineering and the Graduate School of Logistics and Acquisition Management. It describes research interests and faculty expertise; list student theses/dissertations; identifies research sponsors and contributions; and outlines the procedure for contacting either school

Robust Design of RF-MEMS Cantilever Switches Using Contact Physics Modeling

This paper presents the robust design optimization of an RF-MEMS direct contact cantilever switch for minimum actuation voltage and opening time, and maximum power handling capability. The design variables are the length and thickness of the entire cantilever, the widths of the sections of the cantilever, and the dimple size. The actuation voltage is obtained using a 3-D structural-electrostatic finite-element method (FEM) model, and the opening time is obtained using the same FEM model and the experimental model of adhesion at the contact surfaces developed in our previous work. The model accounts for an unpredictable variance in the contact resistance resulting from the micromachining process for the estimation of the power handling. This is achieved by taking the ratio of the root mean square power of the RF current (signal") passing through the switch to the contact temperature ("noise") resulting from the possible range of the contact resistance. The resulting robust optimization problem is solved using a Strength Pareto Evolutionary Algorithm, to obtain design alternatives exhibiting different tradeoffs among the three objectives. The results show that there exists substantial room for improved designs of RF-MEMS direct-contact switches. It also provides a better understanding of the key factors contributing to the performances of RF-MEMS switches. Most importantly, it provides guidance for further improvements of RF-MEMS switches that exploit complex multiphysics phenomena.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87274/4/Saitou7.pd

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Roadmap on signal processing for next generation measurement systems

Signal processing is a fundamental component of almost any sensor-enabled system, with a wide range of applications across different scientific disciplines. Time series data, images, and video sequences comprise representative forms of signals that can be enhanced and analysed for information extraction and quantification. The recent advances in artificial intelligence and machine learning are shifting the research attention towards intelligent, data-driven, signal processing. This roadmap presents a critical overview of the state-of-the-art methods and applications aiming to highlight future challenges and research opportunities towards next generation measurement systems. It covers a broad spectrum of topics ranging from basic to industrial research, organized in concise thematic sections that reflect the trends and the impacts of current and future developments per research field. Furthermore, it offers guidance to researchers and funding agencies in identifying new prospects.AerodynamicsMicrowave Sensing, Signals & System

Nanotools for Neuroscience and Brain Activity Mapping

Neuroscience is at a crossroads. Great effort is being invested into deciphering specific neural interactions and circuits. At the same time, there exist few general theories or principles that explain brain function. We attribute this disparity, in part, to limitations in current methodologies. Traditional neurophysiological approaches record the activities of one neuron or a few neurons at a time. Neurochemical approaches focus on single neurotransmitters. Yet, there is an increasing realization that neural circuits operate at emergent levels, where the interactions between hundreds or thousands of neurons, utilizing multiple chemical transmitters, generate functional states. Brains function at the nanoscale, so tools to study brains must ultimately operate at this scale, as well. Nanoscience and nanotechnology are poised to provide a rich toolkit of novel methods to explore brain function by enabling simultaneous measurement and manipulation of activity of thousands or even millions of neurons. We and others refer to this goal as the Brain Activity Mapping Project. In this Nano Focus, we discuss how recent developments in nanoscale analysis tools and in the design and synthesis of nanomaterials have generated optical, electrical, and chemical methods that can readily be adapted for use in neuroscience. These approaches represent exciting areas of technical development and research. Moreover, unique opportunities exist for nanoscientists, nanotechnologists, and other physical scientists and engineers to contribute to tackling the challenging problems involved in understanding the fundamentals of brain function

Wireless Power Transfer For Biomedical Applications

In this research wireless power transfer using near-field inductive coupling is studied and investigated. The focus is on delivering power to implantable biomedical devices. The objective of this research is to optimize the size and performance of the implanted wireless biomedical sensors by: (1) proposing a hybrid multiband communication system for implantable devices that combines wireless communication link and power transfer, and (2) optimizing the wireless power delivery system. Wireless data and power links are necessary for many implanted biomedical devices such as biosensors, neural recording and stimulation devices, and drug delivery and monitoring systems. The contributions from this research work are summarized as follows: 1. Development of a combination of inductive power transfer and antenna system. 2. Design and optimization of novel microstrip antenna that may resonate at different ultra-high frequency bands including 415 MHz, 905 MHz, and 1300MHz. These antennas may be used to transfer power through radiation or send/receive data. 3. Design of high-frequency coil (13.56 MHz) to transfer power and optimization of the parameters for best efficiency. 4. Study of the performance of the hybrid antenna/coil system at various depths inside a body tissue model. 5. Minimizing the coupling effect between the coil and the antenna through addressed by optimizing their dimensions. 6. Study of the effects of lateral and angular misalignment on a hybrid compact system consisting of coil and antenna, as well as design and optimize the coilâs geometry which can provide maximum power efficiency under misalignment conditions. 7. Address the effects of receiver bending of a hybrid power transfer and communication system on the communication link budget and the transmitted power. 8. Study the wireless power transfer safety and security systems

Design and testing of compact dual-band dual-polarized robust satellite navigation antenna arrays

Die steigende Nachfrage nach präzisen Positionierlösungen für hochautomatisiertes Fahren und sicherheitskritische Anwendungen führt zu der Verwendung von Array-basierten Satellitennavigationsempfängern, die aufgrund des verbesserten Diversity-Gewinns und der potentiellen Strahlformungsfähigkeit eine bessere Leistung aufweisen. Die Notwendigkeit, die Robustheit von Navigationsempfängern gegenüber Quellen von Signalstörungen, wie Mehrwegempfang, atmosphärische, sowie Jamming- und Spoofing, zu verbessern, verlangt, den Empfänger weiter auszubauen, um Polarisations- und Frequenz-Diversity auszunutzen. Das hieraus resultierende Design ist durch eine signifikante Zunahme der Hardware- und Softwarekomplexität gekennzeichnet. Diese Komplexität steigt noch mit dem Trend, den Navigationsempfänger zu miniaturisieren, um die Integration in Fahrzeugen oder mobilen Systemen zu erleichtern. Da die gegenseitige Verkopplung zwischen den Antennenelementen eines kompakten Antennen- Arrays steigt, verschlechtert sich deren Strahlungseffizienz und Polarisationsreinheit und damit die Systemrobustheit. In dieser Arbeit wird ein kompaktes, dualbandiges und dualpolarisiertes Antennenarray für einen Navigationsempfänger untersucht, schaltungstechnisch entworfen und aufgebaut, womit Array-, Frequenz-, und Polarisations-Diversity ermöglicht wird. Dies führt zu einer signifikant verbesserten Robustheit gegenüber den angesprochenen Störungen. Diese Arbeit umfasst das Design des dualbandigen und dualpolarisierten Patchantennenelements, das Design des kompakten Antennenarrays, das Studium der Kreuzpolarisationsquellen in Patchantennen, die Analyse des Einflusses der gegenseitigen Kopplung auf die Strahlungseffizienz und Polarisationsreinheit, und die Abschwächung beider Effekte durch eigenmode-basierten Entkopplungs- und Anpassungsnetzwerken. Darüber hinaus beinhaltet die Arbeit die Integration des Antennensystems mit einem HF-Frontend zur Leistungsverstärkung, Filterung und Signalkonvertierung der Satellitensignale. Die Arbeit umfasst auch die Integration mit einem Array-basierten digitalen Empfänger, in dem neben der Datenerfassung, auch die Richtungsschätzung, das Beamforming und die Anti-Jamming-Algorithmen implementiert wurden. Die Machbarkeit sowohl der Array-Diversity als auch der Polarisations-Diversity wurde in Automotive-related Feldmessungen bestätigt, insbesondere für Elevationswinkel unter 40 bzw. 60 Grad, wo der Einfluss des Mehrwegempfangs ausreichend hohe Pegel erreicht. Die Messungen bestätigten die Robustheit des Empfängers gegenüber Stör- Nutzsignalverhältnissen von bis zu 85 dB und übertrafen damit mehrere "State-of-the-Art" Empfänger.The increasing demand for accurate positioning solutions for highly-automated driving and safety-critical applications motivates the use of array-based satellite navigation receivers that feature better performance, due to the enhanced diversity gain and the potential beamforming capability. The need for improving the robustness of navigation receivers against sources of signal distortion such as multipath propagation, atmospheric impact, jamming, and spoofing violations requests to extend the receiver to exploit polarization and frequency diversities. The resulting design is challenged by the significant rise in hardware and software complexity. This complexity increases even more with the trend to miniaturize the navigation receiver, to ease the integration in vehicles or mobile systems, because mutual coupling rises between the radiating elements of the receiver, and deteriorates their radiation efficiencies and polarization purities, and hence degrades the system robustness. In this thesis, a compact dual-band dual-polarized array-based navigation receiver that uses array diversity, frequency diversity, and polarization diversity is studied and designed, to provide robustness against the different types of distortions. The main contributions of the presented work include the design of the dual-band dual-polarized patch antenna element, the design of the compact antenna array, the study of the cross-polarization sources in patch antennas, the analysis of the mutual coupling impact on radiation efficiency and polarization purity of radiating elements, and the mitigation of both impacts using eigenmode-based decoupling and matching networks. Furthermore, the work also involves the integration of the antenna system with an RF-IF front-end, developed in cooperation with IMMS GmbH, for power amplification, filtering, and down-converting. The dissertation covers also the integration with an array-based digital receiver, developed in cooperation with RWTH Aachen University and the German Aerospace Center (DLR), to implement data acquisition, direction-of-arrival estimation, beamforming, and anti-jamming algorithms. The feasibility of both the array diversity and the polarization diversity was confirmed in automotive-related field measurements, particularly for elevations below 40 and 60 degrees, respectively; i.e., at directions far from the main beam direction of the even mode of the array (at zenith), and where the impact of multipath propagation on strength and polarization of the signal reaches sufficient levels to disturb the receiver. Measurements proved the receiver robustness against jamming-to-signal ratios up to 85 dB, outperforming several state-of-the-art receivers described in literature

Smart Sensor Networks For Sensor-Neural Interface

One in every fifty Americans suffers from paralysis, and approximately 23% of paralysis cases are caused by spinal cord injury. To help the spinal cord injured gain functionality of their paralyzed or lost body parts, a sensor-neural-actuator system is commonly used. The system includes: 1) sensor nodes, 2) a central control unit, 3) the neural-computer interface and 4) actuators. This thesis focuses on a sensor-neural interface and presents the research related to circuits for the sensor-neural interface. In Chapter 2, three sensor designs are discussed, including a compressive sampling image sensor, an optical force sensor and a passive scattering force sensor. Chapter 3 discusses the design of the analog front-end circuit for the wireless sensor network system. A low-noise low-power analog front-end circuit in 0.5μm CMOS technology, a 12-bit 1MS/s successive approximation register (SAR) analog-to-digital converter (ADC) in 0.18μm CMOS process and a 6-bit asynchronous level-crossing ADC realized in 0.18μm CMOS process are presented. Chapter 4 shows the design of a low-power impulse-radio ultra-wide-band (IR-UWB) transceiver (TRx) that operates at a data rate of up to 10Mbps, with a power consumption of 4.9pJ/bit transmitted for the transmitter and 1.12nJ/bit received for the receiver. In Chapter 5, a wireless fully event-driven electrogoniometer is presented. The electrogoniometer is implemented using a pair of ultra-wide band (UWB) wireless smart sensor nodes interfacing with low power 3-axis accelerometers. The two smart sensor nodes are configured into a master node and a slave node, respectively. An experimental scenario data analysis shows higher than 90% reduction of the total data throughput using the proposed fully event-driven electrogoniometer to measure joint angle movements when compared with a synchronous Nyquist-rate sampling system. The main contribution of this thesis includes: 1) the sensor designs that emphasize power efficiency and data throughput efficiency; 2) the fully event-driven wireless sensor network system design that minimizes data throughput and optimizes power consumption