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Active noise control (ANC) has remained a challenging problem in the controls community, even with the rapid development of computers and state-of-the-art digital signal processors (DSP). Despite some limited success in commercial applications, there exists very little published theoretical work that can be used for design purposes. One possible obstacle is that the area of ANC comprises a combination of unrelated backgrounds. In general, a control engineer does not have sufficient knowledge in the physics of acoustics. This may explain why much of the ANC research focuses on adaptive control solutions which does not require deep insight into the acoustics. An adaptive system, however, is nonlinear and has its own open problems. For example, closed-loop stability and achievable performance of an adaptive ANC system cannot be predicted a priori and is generally difficult to analyze. This is the main reason we choose to discuss only linear, fixed-filter ANC systems. In this research we study in detail ANC systems designed to cancel noise in acoustic ducts. Due to the geometry of duct aspect ratio, we can simplify the description of the sound wave propagation along the duct to one-dimensional. Our emphasis is on analysis and design of fixed-controllers using at most two sensors and one actuator. The main thrust of this dissertation is to develop fundamental limitation theories tailored to such duct ANC problems. In particular, we apply the recently developed theories on single-input-two-output (SITO) feedback system. The alignment angle approach is found to be well suited to our ANC setup and has become the main machinery used in the development of stability and performance analysis, as well as in the selection of sensor and actuator locations. We present a new tradeoff between closed-loop stability margins and achievable performance resulting from constraints imposed by certain duct configurations. This inherent limitation can be hard to overcome with one-sensor design schemes such as feedforward controllers prevalently used in ANC literature. We demonstrate via analysis and simulations the advantages of using a two-input-single-output (TISO) controller.

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Apex-Adams-Simulink co-simulation is applied to active magnetic bearing (AMB) rotors, demonstrating results unshown in literature, including continuous frequency response, and unavailable in known rotor dynamics software, including touchdown bearing impact. AMBs levitate rotors without contact, so they involve no friction, wear, lubrication, pollution, or shaft speed limits and are thus valuable for large, high-speed applications. Modeling of such rotors, necessary for safety and performance, simultaneously requires flexible body dynamics and advanced control design, but simulation programs tend to specialize in only one or the other. The co-simulation method combines multiple such programs—MSC Apex (finite element modeling), Adams (multibody dynamics), and Simulink (graphical control design) with MATLAB (visualization tools)—expanding the design space for AMB rotor modeling beyond that of available commercial software. In this work, accuracy of co-simulation to theory is validated through a rigid AMB rotor and a hanging disk on a steel wire, and new results are shown for a flexible anisotropic rotor and a simplified touchdown bearing impact test.

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Active sensors, such as radar, lidar, and sonar, emit signals into the environment and analyze the reflections to gather information such as distance, bearing, and, with more complex processing, shape and material. Conversely, passive sensors such as microphones and cameras, rely on signals produced by objects in the environment to collect data. This deprives the sensors of the ability to directly detect distance unless used in arrays, but affords them the benefits of being concealed and saving energy. In modern applications, we see active sensors filtering out any signals not originating from their transducers as if they were noise. However, contemporary research has shown that echolocating bats have the capability of taking advantage of both active and passive echolocation. By fusing the information a bat can gather from a conspecific's echoes with their own, it is suggested that more data may become available to the eavesdropping bat. Taking bioinspiration from these suggested abilities, we seek to explore the question of how fusing active and passive ultrasonic sensing may effect the information available to a robotic vehicle. Our first investigation was an experimental verification of the capabilities of a stereo sensor for passively tracking an ultrasonic sound source using limited a priori information about the target being tracked. Our results pos- itively supported a previous simulation study and showed that the Bayesian estimator was further able to recover from divergences due to hardware and software limitations. Break- ing from the limited assumptions of the previous work, we began a full investigation of the fusion of active and passive sensing with a numerical investigation of the effects of these sensing techniques on a robotic vehicle performing simultaneous localization and mapping (SLAM). The SLAM problem consists of robot that is placed in an unknown environment, which it proceeds to map and localize itself within. By ensonifying the environment with a stationary beacon, we compared the performance of the vehicle when using active, passive, and fused sensing strategies. Building upon previous numerical simulations, we found supporting evidence that, when information available through active sensing is limited, incorporating passive measurements improves the information available to the vehicle and may also improve the accuracy of its map and localization. Finally, we took the first step to fully realizing our initial goal by numerically investigating robotic eavesdropping on two dynamics vehicles. This work showed promising results for the continued investigation of fused sensing strategies and also highlighted the importance of formation control and landmark initialization. / Doctor of Philosophy / While the stereotype of bats being blind is a fallacy, it is true many species rely on their abilities of echolocation to navigate their surrounding environment. It has been observed that bats not only use the echoes of their own vocalizations to gather this information but also may eavesdrop on the echoes of other bats in their immediate area. This suggests that bats have the ability to effectively use two types of sensing at once, which are categorized as active and passive sensing. Active sensors are defined by their need to create signals that are sent out to the environment while passive sensors rely on signals they can collect from the environment to understand it. In this work we investigate the question: can robots that combine active and passive sensing capabilities into a single sensor gain more effective information about their environment? The first problem we investigate is an experimental proof of concept that it is possible to passively track an acoustic emitter without direct knowledge of how it is moving. Using a simple two microphone sensor we show support for previously tested numerical results that this form of tracking is possible. Moving away from this constrained system our later work uses modeling and simulation of the simultaneous localization and mapping (SLAM) problem in robotics to gain more understanding of the question above.

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This Research Report presents some of the equations of underwater acoustics that relate to the signal excess noise received by a transducer. The basic structural equation is developed, as are defining equations for each term in that equation. An analysis is performed utilizing typical values to ascertain if the elements of the structural equation can be simplified. Results delineate that several terms of that equation can be neglected while maintaining a relative high degree of accuracy.