Scott A. Miller

Five parametric resonances in a microelectromechanical system

The Mathieu equation governs the forced motion of a swing, the stability of ships and columns, Faraday surface wave patterns on water,, the dynamics of electrons in Penning traps, and the behaviour of parametric amplifiers based on electronic or superconducting devices. Theory predicts that parametric resonances occur near drive frequencies of 2ω0/n, where ω0 is the systems natural frequency and n is an integer ⩾1. But in macroscopic systems, only the first instability region can typically be observed, because of damping and the exponential narrowing of the regions with increasing n. Here we report parametrically excited torsional oscillations in a single-crystal silicon microelectromechanical system. Five instability regions can be measured, due to the low damping, stability and precise frequency control achievable in this system. The centre frequencies of the instability regions agree with theoretical predictions. We propose an application that uses parametric excitation to reduce the parasitic signal in capacitive sensing with microelectromechanical systems. Our results suggest that microelectromechanical systems can provide a unique testing ground for dynamical phenomena that are difficult to detect in macroscopic systems.

A POMDP framework for coordinated guidance of autonomous UAVs for multitarget tracking

This paper discusses the application of the theory of partially observable Markov decision processes (POMDPs) to the design of guidance algorithms for controlling the motion of unmanned aerial vehicles (UAVs) with onboard sensors to improve tracking of multiple ground targets. While POMDP problems are intractable to solve exactly, principled approximation methods can be devised based on the theory that characterizes optimal solutions. A new approximation method called nominal belief-state optimization (NBO), combined with other application-specific approximations and techniques within the POMDP framework, produces a practical design that coordinates the UAVs to achieve good long-term mean-squared-error tracking performance in the presence of occlusions and dynamic constraints. The flexibility of the design is demonstrated by extending the objective to reduce the probability of a track swap in ambiguous situations.

Integrated micro‐scanning tunneling microscope

Two versions of micro‐scanning tunneling microscopes (micro‐STMs) have been fabricated. The integrated micro‐STMs are fabricated from single crystal silicon using the high‐aspect‐ratio SCREAM process. Each micro‐STM includes integrated xy comb drive actuators and a torsional z actuator with integrated cantilever and tip. One micro‐STM measures approximately 200 μm on‐a‐side and is an example of a STM element for a STM array architecture. Another, larger micro‐STM/atomic force microscope measures 2 mm on‐a‐side including a 1 mm long cantilever with a 20 nm diam tip. We demonstrate the operation of this larger STM by obtaining a STM image of a 200 nm metal conductor on a silicon chip.

Coordinated guidance of autonomous uavs via nominal belief-state optimization

We apply the theory of partially observable Markov decision processes (POMDPs) to the design of guidance algorithms for controlling the motion of unmanned aerial vehicles (UAVs) with on-board sensors for tracking multiple ground targets. While POMDPs are intractable to optimize exactly, principled approximation methods can be devised based on Bellmans principle.We introduce a new approximation method called nominal belief-state optimization (NBO). We show that NBO, combined with other application-specific approximations and techniques within the POMDP framework, produces a practical design that coordinates the UAVs to achieve good long-term mean-squared-error tracking performance in the presence of occlusions and dynamic constraints.

Micromechanical cantilevers and scanning probe microscopes

We have fabricated two microelectromechanical scanning tunneling microscopes (Micro- STMs) with 3D (xyz) actuators and integrated high aspects ratio tips. The reduction in the size of scanning probe microscopes allows for faster scanning speeds, array architectures, and massively parallel operation. The two Micro-STMs are fabricated from single crystal silicon using the high-aspect-ratio SCREAM process and are small enough to be used in array architectures. The torsional cantilever design used for out-of-plane (z) motion can be easily be adapted to scanning force microscopy. Typical atomic force microscope cantilevers have spring constants on the order of 0.01 - 10 N/m. To produce cantilevers with lower spring constants, ordinary thin film techniques would require longer (several mm) and thinner (sub- micrometers ) cantilevers. A mechanical analysis of torsional cantilevers reveals that high aspect ratio rectangular beams, such as the ones we fabricate, are easily twisted. By using the torsional design, we can achieve lower spring constants (10-1 - 10-7 N/m) without having to make a very thin film cantilever. We have demonstrated torsional cantilevers with spring constants on the order of 10-2 N/m. These cantilevers can be used as extremely sensitive force sensors for atomic force microscopy.

Scaling torsional cantilevers for scanning probe microscope arrays: theory and experiment

An array (12/spl times/12) of microelectromechanical probe tips with integrated actuators and capacitive sensors for scanning probe microscopy has been designed, fabricated, and characterized. Each array element consists of a single crystal silicon tip on a torsional cantilever with out-of-plane interdigitated electrode capacitors. The size of each array element is about 150 /spl mu/m by 150 /spl mu/m with a tip-to-tip spacing in the array of 200 /spl mu/m. Given these dimensions, the packing density of the devices is about 2500 units/cm/sup 2/. The out-of-plane torsional design allows for significant improvement in performance (larger tip displacement and increased sense capacitance) and a higher density of devices per unit area as the minimum feature size (MFS) decreases.

Surface micromachined interferometer‐based optical reading technique

A surface micromachined suspended interferometer and an atomic force microscope (AFM) are incorporated into a novel optical reading technique. The AFM tip mechanically deflects the suspended membrane as it scans past a data bit on the membrane surface. The data are read by monitoring the changing interference pattern generated in the optical aperture of the interferometer. When operated in parallel, there exists the potential for high speed, high density data reading.

Optical reading and writing on GaAs using an atomic force microscope

Optically aided reading and writing of gold and tungsten mounds on proton‐implanted, multiple quantum well InGaAs/GaAs wafers has been demonstrated using an atomic force microscope (AFM). The system is relatively simple, requiring only a diode laser as the light source, providing a novel, compact, optoelectronic memory system.

On Bellman’s principle with inequality constraints

We consider an example by Haviv (1996) of a constrained Markov decision process that, in some sense, violates Bellmans principle. We resolve this issue by showing how to preserve a form of Bellmans principle that accounts for a change of constraint at states that are reachable from the initial state.

Flow-rate control for managing communications in tracking and surveillance networks

This paper describes a primal-dual distributed algorithm for managing communications in a bandwidth-limited sensor network for tracking and surveillance. The algorithm possesses some scale-invariance properties and adaptive gains that make it more practical for applications such as tracking where the conditions change over time. A simulation study comparing this algorithm with a priority-queue-based approach in a network tracking scenario shows significant improvement in the resulting track quality when using flow control to manage communications.