Tracy Dean Hudson

A wide dynamic range Silicon-on-Insulator MEMS gyroscope with digital force feedback

This paper presents development efforts and initial test data for a Silicon-on-Insulator (SOI) Micro Electro Mechanical System (MEMS), vibratory angular rate sensor intended for hypervelocity and small diameter missiles and munitions. The SOI angular rate sensor (gyroscope), intended for wide dynamic range and harsh environment applications, utilizes advantages offered from the mass and feature sizes achieved by Deep Reactive Ion Etching (DRIE). This particular effort is focused on developing a symmetric device design along with multi-bit sigma-delta force-feedback control to increase dynamic range and reduce susceptibility to environmental parameters, including temperature, vibration, and sustained Z-axis acceleration loading. A prototype, single layer MEMS chip, consisting of a proof mass placed in a three-fold mode-decoupled symmetric suspension, has been fabricated and tested. The mode-decoupled suspension allows only one degree of in-plane motion for each comb drive, thereby attenuating errors due to oscillation axis misalignment. In addition, suspension symmetry maintains matched oscillation mode frequencies through processing and temperature variations, allowing maximized dynamic range in the discrete-time control loop. Attached to the suspension are comb-drives operating in their linear mode. Use of these actuators eliminates deflection-induced nonlinearity in the control loop. The rate sensing performance of these devices in an open-loop configuration has been characterized, and a unit is being flight-tested on a prototype hypervelocity missile. Current efforts will reduce random walk through preamp optimization, add an excitation control loop to improve bias stability, and implement the digital feedback loop to increase dynamic range. This paper presents recent development efforts and initial test data for the SOI-based angular rate sensor, intended for small diameter missiles and munitions applications.

Single-layer silicon-on-insulator MEMS gyroscope for wide dynamic range and harsh environment applications

The Army Aviation and Missile Command (AMCOM), Morgan Research Corporation, and Aegis Research Corporation are developing an SOI-based vibratory-rate z-axis MEMS gyroscope utilizing force-feedback control, and intended for wide dynamic range and harsh environment applications. Rate sensing in small diameter ballistic missile guidance units requires a rate resolution of less than 1 degree(s)/hr over a range of -3000 to +3000 degree(s)/sec, resulting in a dynamic range of 107. In addition, the devices must operate through military specifications on temperature (-55 degree(s)C to +125 degree(s)C) and vibration (1000 g at 5 - 15 kHz). This paper presents modeling, simulation, and fabrication efforts, as well as initial test data, for an SOI-based rate sensor intended for this application. The prototyped gyroscope is a single layer structure consisting of a proof mass placed in a three-fold mode-decoupled symmetric suspension. The device is fabricated in a cost-effective and highly-controllable Silicon-on-Insulator (SOI) process for in-plane inertial devices. The mechanical structure is integrated in a vacuum-sealed hermetic package with a separate CMOS readout ASIC. At the present time, the device has undergone two design iterations, with the most recent just completed.

High-performance microfabricated angular rate sensor

The development of a miniature angular rate sensor based on silicon-on-insulator (SOI) microfabrication technology is presented. The design, fabrication, integration, and inertial testing of a MEMS-based angular rate sensor with large dynamic range were the driving forces behind this research. The design goals of 10-deg/h bias stability while operating through 2000-deg/s roll environments are presented. The sensor design is based on a straightforward single-mask fabrication approach that utilizes deep reactive ion etching of a 100-µm-thick device layer, with a buried 2- to 3-µm oxide layer used as the sacrificial layer, in an SOI substrate. To date, the data show demonstrated bias drift performance of 60 deg/h over this fast-roll environment.

Integrated PCB active cooling with piezoelectric actuator

Thermal management is challenging in RF communication and radar systems that require high-power levels for operation and reliability as well as small footprints to control intrinsic losses and meet design constraints. An interesting approach uses discrete, in-situ fluid handling and embedded synthetic jet drivers to enhance local cooling at the component. In this approach, fluid cavities and actuators are integrated into the PCB near the component. Magnetic and piezoelectric actuators have proven effective in other less-demanding applications. The challenge to adapting from magnetic to piezoelectric actuators is to achieve high flowrates because piezo-actuators have lower displacement and higher frequencies. This investigation explores frequency and displacement effects on cooling rates for piezo-actuators embedded in PCB. Further concept development includes integration with thermal ground planes.

Optimization of MEMS Ku-band phase shifter

Summary form only given. Microelectromechanical system (MEMS) switches and phase shifters built from these switches have been demonstrated in several papers (Guan-Leng Tan et al., 2002, 2003; Hacker, J.B. et al., 2003; Kim, M. et al., 2001; Pillans, B. et al., 1999). Potential applications include: military radar, including active and passive electronically scanned arrays; aviation radar; reconfigurable wireless networks; satellite broadband communication networks. MEMS phase shifters offer low insertion loss and parasitics. In addition, the MEMS phase shifters may provide cost and weight advantages for large arrays. The poster addresses the optimization of a 15 GHz switched-line phase shifter in which every delay bit is implemented separately. The size of the phase shifter is one area to be optimized. Also, it is intended to develop a hybrid design to reduce the number of switches in the phase shifter.

Measurement of spatial light modulator parameters

An investigation is made of means to the standardization of methods for parameter characterization in the cases of spatial light modulators of optically addressed, electrically addressed, amplitude-modulating, and phase-modulating types, with a view to recommendations for future practice. The speed, resolution, and visibility parameters are noted to compare well irrespective of modulator type; phase and amplitude modulating devices cannot be directly compared, however, due to the fundamentally different ways that parameters are measured for each. To be meaningful, the MTF for an optically-addressed device must be accompanied by speed and illumination data. Lifetimes should be specified for all devices.

Optical evaluation of the microchannel spatial light modulator

The spatial light modulator (SLM) is a critical element in most optical processing systems. Different devices on the market today include the Hughes Liquid Crystal Light Valve (LCLV), the Ferroelectric LCLV, the GEC-Marconi LCLV, the Semetex MOSLM, Liquid Crystal Televisions, and the Deformable Mirror Device. The parameters of the above modulators have been evaluated at the Army Missile Commands Photonics and Optical Sciences Labs at Redstone Arsenal in an effort to determine the utility of these modulators as image transducers in optical correlator architectures. This paper will focus on another device perhaps applicable to optical correlators, the Microchannel Spatial Light Modulator (MSLM). The results of speed, maximum resolution, and visibility measurements will be presented.

MEMS-based spectral decomposition of acoustic signals

Many embedded structural monitoring applications require extremely low-power sensors and signal processing capabilities. In particular, the continuous monitoring of vibrations, impacts, and acoustic noise within a structure typically requires significant power for not only the transducers themselves, but also the signal conditioning, analog to digital conversion, and digital signal processing necessary to extract useful information from the captured waveforms [1,2,3,4]. This paper presents a sensor methodology that performs spectral decomposition of acoustic and vibration waveforms using arrays of micromechanical resonant structures, mechanical filters, and embedded active films, with signal processing being performed in the mechanical domain. The use of embedded active films in these devices results in sensors that can be, in some instances, self-powered by the vibrations being detected. A MEMS-based acoustic emission spectral sensor employing an embedded electret film has been fabricated and tested in an impact environment. Sensor fabrication was performed using in situ polarization of the active film after completing the entire fabrication flow. This sensor consisted of an array of tuned micromechanical resonant elements with natural frequencies varying across the spectrum of interest. The sensor was incorporated into a ball drop apparatus in which controlled acoustic pulses could be delivered to the structure under test. Spectral output from the sensor was collected and could be used to distinguish between impacts involving different material sets and impact energies without the use of digital signal processing and its associated power consumption.

Microfabrication technologies for missile components

This invited communication presents the microfabrication technologies, and associated issues, being developed by the U.S. Army’s AMRDEC for missile components. Primary components are inertial sensors and radio frequency switches. Two inertial sensor types are discussed -- fiber optic and micro-electromechanical system (MEMS) gyroscopes. The RF switches are also based on MEMS technology and are a natural extension of the microfabrication processes developed for the MEMS gyroscope.

Integrated localized cooling using piezoelectrically-driven synthetic jets

RF communications and radar systems are comprised of tightly packaged high wattage components requiring a controlled temperature to meet performance and reliability parameters. As these systems are becoming smaller and more powerful, existing thermal management technology limits system performance. An approach being pursued to address thermal management issues is localized synthetic jet die-level cooling using embedding piezoelectric actuators within the electronic assembly. U.S. Army AMRDEC is developing and testing piezocomposite actuator test beds to mature the concepts and develop practical solutions. This investigation has demonstrated Lightweight Piezocomposite Curved Actuator (LiPCA) devices as low-frequency, small form factor, high-displacement, and high flow rate sources for synthetic jet cooling. The goal of the investigation is to achieve thermal management using higher efficiency and smaller actuators than demonstrated in previous synthetic jet efforts.