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Automatic Control, IEEE Transactions on

Issue 6 • Date July 2008

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  • Table of contents

    Publication Year: 2008 , Page(s): C1 - C4
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  • IEEE Transactions on Automatic Control publication information

    Publication Year: 2008 , Page(s): C2
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  • Scanning the issue

    Publication Year: 2008 , Page(s): 1337 - 1338
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  • In Memoriam: George S. Axelby(1918–2008)

    Publication Year: 2008 , Page(s): 1339 - 1340
    Cited by:  Papers (1)
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  • A Linear Programming Approach to the Synthesis of Fixed-Structure Controllers

    Publication Year: 2008 , Page(s): 1341 - 1352
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    This paper describes a new approach to the synthesis of fixed-structure and fixed-order controllers. Such controllers are required in many practical applications. A broad class of fixed-structure controller synthesis problems can be reduced to the determination of a real controller parameter vector (or simply, a controller) K=(k 1, k 2, ... , k t), so that a given set of real or complex polynomials of the form P(s,K):=Po(s)+k 1 P 1(s)+... +k t P t(s) is Hurwitz. The stability of the closed-loop system requires a real characteristic polynomial to be Hurwitz, while several performance criteria can be satisfied by ensuring that a family of complex polynomials is Hurwitz. A novel feature of this paper is the exploitation of the interlacing property (IP) of Hurwitz polynomials to construct arbitrarily tight approximations of the set of stabilizing controllers. This is done by systematically constructing sets of linear inequalities in K. The union of the feasible sets of linear inequalities provides an approximation of the set of all controllers K, which render P(s, K) Hurwitz. As the number of sets of linear inequalities increases and approaches infinity, we show that the union of the feasible sets approaches the set of all stabilizing controllers of the desired structure. The main tools that are used in the construction of the sets of linear inequalities are the Hermite-Biehler theorem, Descartes' rule of signs, and its generalization. We provide examples of the applicability of the proposed methodology to the synthesis of fixed-order stabilizing controllers. View full abstract»

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  • Controller Synthesis Free of Analytical Models: Three Term Controllers

    Publication Year: 2008 , Page(s): 1353 - 1369
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1263 KB) |  | HTML iconHTML  

    The main focus of this paper is on direct data driven synthesis and design of controllers. We show that the complete set of stabilizing proportional-integral-derivative (PID) and first-order controllers for a finite dimensional linear time-invariant plant, possibly cascaded with a delay, can be calculated directly from the frequency response (Nyquist/Bode) data P(jomega) for omega epsi [0, infin) without the need of producing an identified analytical model. It is also shown that complete sets achieving guaranteed levels of performance measures such as gain margin, phase margin, and Hinfin norms can likewise be calculated directly from only Nyquist/Bode data. The solutions have important new features. For example it is not necessary to know the order of the plant or even the number of left half plane or right half plane poles or zeros. The solution also identifies, in the case of PID controllers an exact low frequency band over which the plant data must be known with accuracy and beyond which the plant information may be rough or approximate. These constitute important new guidelines for identification when the latter is to be used for control design. The model free approach to control synthesis and design developed here is an attractive complement to modern and post modern model based design methods which require complete information on the plant and generally produce a single optimal controller. A discussion is included, with illustrative example, of the sharp differences between model-free and model based approaches when computing sets of stabilizing controllers. For example, it is shown, that the identified model of a high order system can be non-PID stabilizable whereas the original data indicates it is PID stabilizable. The results given here are also a significant improvement over classical control loop-shaping approaches since we obtain complete sets of controllers achieving the design specifications. It can enhance fuzzy and neural approaches which are model- - free but cannot guarantee stability and performance. Finally, these results open the door to adaptive, model free, fixed order designs of real world systems. View full abstract»

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  • Vehicle Platoons Through Ring Coupling

    Publication Year: 2008 , Page(s): 1370 - 1377
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (451 KB) |  | HTML iconHTML  

    In this paper, a novel strategy for the control of a string of vehicles is designed. The vehicles are coupled in a unidirectional ring at the interaction level: each vehicle is influenced by the position of its immediate forward neighbor; the first vehicle in the platoon is influenced by the position of the last vehicle. Through these interactions a cooperative behavior emerges and a platoon of vehicles moving at a constant velocity with constant inter-vehicle spacings is formed. This contrasts with more traditional control schemes where an independent leader vehicle is followed by the remaining vehicles. View full abstract»

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  • Traveling Salesperson Problems for the Dubins Vehicle

    Publication Year: 2008 , Page(s): 1378 - 1391
    Cited by:  Papers (29)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (747 KB) |  | HTML iconHTML  

    In this paper, we study minimum-time motion planning and routing problems for the Dubins vehicle, i.e., a nonholonomic vehicle that is constrained to move along planar paths of bounded curvature, without reversing direction. Motivated by autonomous aerial vehicle applications, we consider the traveling salesperson problem for the Dubins vehicle (DTSP): given n points on a plane, what is the shortest Dubins tour through these points, and what is its length? First, we show that the worst-case length of such a tour grows linearly with n and we propose a novel algorithm with performance within a constant factor of the optimum for the worst-case point sets. In doing this, we also obtain an upper bound on the optimal length in the classical point-to-point problem. Second, we study a stochastic version of the DTSP where the n targets are randomly and independently sampled from a uniform distribution. We show that the expected length of such a tour is of order at least n 2/3 and we propose a novel algorithm yielding a solution with length of order n 2/3 with probability one. Third and finally, we study a dynamic version of the DTSP: given a stochastic process that generates target points, is there a policy that guarantees that the number of unvisited points does not diverge over time? If such stable policies exist, what is the minimum expected time that a newly generated target waits before being visited by the vehicle? We propose a novel stabilizing algorithm such that the expected wait time is provably within a constant factor from the optimum. View full abstract»

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  • Optimal Sensor Querying: General Markovian and LQG Models With Controlled Observations

    Publication Year: 2008 , Page(s): 1392 - 1405
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB) |  | HTML iconHTML  

    This paper is motivated by networked control systems deployed in a large-scale sensor network where data collection from all sensors is prohibitive. We model it as a class of discrete-time stochastic control systems for which the observations available to the controller are not fixed, but there are a number of options to choose from, and each choice has a cost associated with it. The observation costs are added to the running cost of the optimization criterion and the resulting optimal control problem is investigated. Since only part of the observations are available at each time step, the controller has to balance the system performance with the penalty of the requested information (query). We first formulate the problem for a general partially observed Markov decision process model and then specialize to the stochastic linear quadratic Gaussian problem. We focus primarily on the ergodic control problem and analyze this in detail. View full abstract»

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  • An Approximate Simulation Approach to Symbolic Control

    Publication Year: 2008 , Page(s): 1406 - 1418
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1900 KB) |  | HTML iconHTML  

    This paper introduces a methodology for the symbolic control of nonlinear systems based on an approximate notion of simulation relation. This notion generalizes existing exact notions of simulation and is completely characterized in terms of known stabilizability concepts. Equipped with this notion we show how, under certain stabilizability assumptions, we can construct finite or symbolic models for nonlinear control systems. Synthesizing controllers for the original control system can then be done by using supervisory control techniques on the finite models and by refining the resulting finite controllers to hybrid controllers enforcing the specification on the original continuous control system. The proposed design methodology can be seen as a correct-by-design way of obtaining both the feedback control laws as well as the control software responsible for deciding which law is executed and when. View full abstract»

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  • A Dynamic Pickup and Delivery Problem in Mobile Networks Under Information Constraints

    Publication Year: 2008 , Page(s): 1419 - 1433
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB) |  | HTML iconHTML  

    This paper considers a network in which a set of vehicles is responsible for picking up and delivering messages that arrive according to a Poisson process. Message pickup and delivery locations are uniformly distributed in a convex region. The vehicles are required to pickup and deliver the messages so that the average delay is minimized. It is required that the vehicle that picks up a message must be the one to deliver it. This problem is called the dynamic pickup and delivery problem (DPDP) and has applications in the context of autonomous vehicles and wireless ad hoc networks. The control policies considered are separable into two parts: an assignment policy used by a centralized controller to assign arriving messages to the vehicles for service and a service policy used by each vehicle to determine the service routes through its assigned messages. Lower bounds are provided on the delay achievable by separable control policies that depend on the information constraints in place. It is proved that the optimal average delay scaling can be reduced when message destination information is available to the centralized controller in addition to the message source information. The paper also provides policies that achieve these scaling bounds, proving that these bounds are tight. View full abstract»

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  • Cooperative Control of Multiple Nonholonomic Mobile Agents

    Publication Year: 2008 , Page(s): 1434 - 1448
    Cited by:  Papers (59)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (906 KB) |  | HTML iconHTML  

    This paper considers two cooperative control problems for nonholonomic mobile agents. In the first problem, we discuss the design of cooperative control laws such that a group of nonholonomic mobile agents cooperatively converges to some stationary point under various communication scenarios. Dynamic control laws for each agent are proposed with the aid of sigma-processes and results from graph theory. In the second problem, we discuss the design of cooperative control laws such that a group of mobile agents converges to and tracks a target point which moves along a desired trajectory under various communication scenarios. By introducing suitable variable transformations, cooperative control laws are proposed. Since communication delay is inevitable in cooperative control, in each of the above cooperative control problems, we analyze the effect of delayed communication on the proposed controllers. As applications of the proposed results, formation control of wheeled mobile robots is discussed. It is shown that our results can be successfully used to solve formation control problem. To show effectiveness of the proposed approach, simulation results are included. View full abstract»

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  • Supervisory Control Architecture for Discrete-Event Systems

    Publication Year: 2008 , Page(s): 1449 - 1461
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB) |  | HTML iconHTML  

    A flexible decentralized and hierarchical architecture is presented to reduce computational effort in designing optimal nonblocking supervisors for discrete-event systems (DES). We organize a DES into modular subsystems that embody internal interacting dependencies. Verification of, and coordination among modular subsystems are achieved through their model abstractions. Sufficient conditions are presented to guarantee that coordinators and modular supervisors result in maximally permissive and nonblocking control. A medium-sized example demonstrates the computational effectiveness of our approach. View full abstract»

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  • Stochastic Approximation Approaches to the Stochastic Variational Inequality Problem

    Publication Year: 2008 , Page(s): 1462 - 1475
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    Stochastic approximation methods have been extensively studied in the literature for solving systems of stochastic equations and stochastic optimization problems where function values and first order derivatives are not observable but can be approximated through simulation. In this paper, we investigate stochastic approximation methods for solving stochastic variational inequality problems (SVIP) where the underlying functions are the expected value of stochastic functions. Two types of methods are proposed: stochastic approximation methods based on projections and stochastic approximation methods based on reformulations of SVIP. Global convergence results of the proposed methods are obtained under appropriate conditions. View full abstract»

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  • Structural Properties of Optimal Transmission Policies Over a Randomly Varying Channel

    Publication Year: 2008 , Page(s): 1476 - 1491
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (639 KB) |  | HTML iconHTML  

    We consider the problem of transmitting packets over a randomly varying point to point channel with the objective of minimizing the expected power consumption subject to a constraint on the average packet delay. By casting it as a constrained Markov decision process in discrete time with time-averaged costs, we prove structural results about the dependence of the optimal policy on buffer occupancy, number of packet arrivals in the previous slot and the channel fading state for both i.i.d. and Markov arrivals and channel fading. The techniques we use to establish such results: convexity, stochastic dominance, decreasing-differences, are among the standard ones for the purpose. Our main contribution, however, is the passage to the average cost case, a notoriously difficult problem for which rather limited results are available. The novel proof techniques used here are likely to have utility in other stochastic control problems well beyond their immediate application considered here. View full abstract»

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  • {cal H}_{\infty } Output-Feedback Control Based on an FIR-Type Quasi-Deadbeat Observer

    Publication Year: 2008 , Page(s): 1492 - 1498
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB) |  | HTML iconHTML  

    This technical note proposes a novel output-feedback control law based on a finite impulse response (FIR)-type quasi-deadbeat observer for linear systems. For nominal systems without disturbances, this technical note first establishes the deadbeat condition that reduces the state estimation error to zero within a finite time and verifies that all the hidden poles of the closed-loop system under the quasi-deadbeat observer-based control law are zero and that the separation principle holds true. In order to enhance the disturbance rejection capability for systems with random-work disturbances, on the structural merit of the FIR-type observer, we have proposed the conditions for an H infin quasi-deadbeat observer and an H infin stabilizer based on the predetermined observer, respectively. View full abstract»

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  • Stabilization of Approximately Feedback Linearizable Systems Using Singular Perturbation

    Publication Year: 2008 , Page(s): 1499 - 1503
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB) |  | HTML iconHTML  

    We consider a stabilization problem of approximately feedback linearizable systems. We introduce a perturbation parameter by applying high-gain feedback and use both the feedback linearization method and the singular perturbation method for the controller design. Through this, we can overcome the rigorous conditions of the feedback linearization method and can reduce the dimension of the slow model of the singularly perturbed system. View full abstract»

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  • On Consensus Algorithms for Double-Integrator Dynamics

    Publication Year: 2008 , Page(s): 1503 - 1509
    Cited by:  Papers (207)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (595 KB) |  | HTML iconHTML  

    This note considers consensus algorithms for double-integrator dynamics. We propose and analyze consensus algorithms for double-integrator dynamics in four cases: 1) with a bounded control input, 2) without relative velocity measurements, 3) with a group reference velocity available to each team member, and 4) with a bounded control input when a group reference state is available to only a subset of the team. We show that consensus is reached asymptotically for the first two cases if the undirected interaction graph is connected. We further show that consensus is reached asymptotically for the third case if the directed interaction graph has a directed spanning tree and the gain for velocity matching with the group reference velocity is above a certain bound. We also show that consensus is reached asymptotically for the fourth case if and only if the group reference state flows directly or indirectly to all of the vehicles in the team. View full abstract»

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  • Perfect Elimination of Regulation Transients in Discrete-Time LPV Systems via Internally Stabilizable Robust Controlled Invariant Subspaces

    Publication Year: 2008 , Page(s): 1509 - 1515
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (498 KB) |  | HTML iconHTML  

    This note introduces a geometric solution to the problem of perfect elimination of regulation transients in discrete-time, linear systems subject to swift and wide, a priori-known, parameter variations. The constructive proof of the conditions for problem solvability requires a preliminary, strictly geometric interpretation of the multivariable autonomous regulator problem, specifically aimed at discrete-time, linear systems. The novel concept of internal stabilizability of a robust controlled invariant subspace plays a key role in the formulation of those conditions as well as in the synthesis of the control scheme. View full abstract»

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  • Unit Quaternion-Based Output Feedback for the Attitude Tracking Problem

    Publication Year: 2008 , Page(s): 1516 - 1520
    Cited by:  Papers (46)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (661 KB) |  | HTML iconHTML  

    In this note, we propose a quaternion-based dynamic output feedback for the attitude tracking problem of a rigid body without velocity measurement. Our approach consists of introducing an auxiliary dynamical system whose output (which is also a unit quaternion) is used in the control law together with the unit quaternion representing the attitude tracking error. Roughly speaking, the necessary damping that would have been achieved by the direct use of the angular velocity can be achieved, in our approach, by the vector part mathtilde q of the error signal between the output of the auxiliary system and the unit quaternion tracking error. The resulting velocity-free control scheme guarantees almost global asymptotic stability which is as strong as the topology of the motion space can permit. In the regulation case, our control law is a pure quaternion feedback (i.e., consisting of two terms that are vector parts of unit-quaternion), and hence, the control torques are naturally bounded by the control gains. Simulation results are provided to show the effectiveness of the proposed control scheme. View full abstract»

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  • Robust Control of Nonlinear Jump Parameter Systems Governed by Uncertain Chains

    Publication Year: 2008 , Page(s): 1520 - 1526
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    We consider an infinite-horizon minimax optimal control problem for stochastic uncertain systems governed by a discrete-state uncertain continuous-time chain. Using existing risk-sensitive control results, a robust suboptimal absolutely stabilizing guaranteed cost controller is constructed. Conditions are presented under which this suboptimal controller is minimax optimal. We then present a numeric algorithm for calculating a robust (sub)optimal controller using a Markov chain approximation technique. View full abstract»

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  • Input-to-State Stability of Time-Delay Systems: A Link With Exponential Stability

    Publication Year: 2008 , Page(s): 1526 - 1531
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (425 KB) |  | HTML iconHTML  

    The main contribution of this technical note is to establish a link between the exponential stability of an unforced system and the input-to-state stability (ISS) via the Liapunov-Krasovskii methodology. It is proved that a system which is (globally, locally) exponentially stable in the unforced case is (globally, locally) input-to-state stable when it is forced by a measurable and locally essentially bounded input, provided that the functional describing the dynamics in the unforced case is (globally, on bounded sets) Lipschitz and the functional describing the dynamics in the forced case satisfies a Lipschitz-like hypothesis with respect to the input. Moreover, a new feedback control law is provided for delay-free linearizable and stabilizable time-delay systems, whose dynamics is described by locally Lipschitz functionals, by which the closed-loop system is ISS with respect to disturbances adding to the control law, a typical problem due to actuator errors. View full abstract»

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  • Off-Line Reference Shaping of Periodic Trajectories for Constrained Systems With Uncertainties

    Publication Year: 2008 , Page(s): 1531 - 1535
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (565 KB) |  | HTML iconHTML  

    This paper is concerned with off-line reference shaping of infinite horizon periodic trajectories for uncertain closed-loop systems with state/input constraints. The method allows us to improve tracking performance subject to constraints in the presence of uncertainties. First, the reference shaping for nominal systems is proposed, which yields a suboptimal solution through decomposition of the infinite horizon tracking problem into two finite ones. Second, the method is extended to fulfill the constraints robustly. View full abstract»

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  • Design of Switched Linear Systems in the Presence of Actuator Saturation

    Publication Year: 2008 , Page(s): 1536 - 1542
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1106 KB) |  | HTML iconHTML  

    For a group of linear systems, each under a saturated linear, not necessarily stabilizing, feedback law, we design a switching scheme such that the resulting switched system is locally asymptotically stable at the origin with a large domain of attraction. By expressing each saturated linear feedback in a convex hull of a group of auxiliary linear feedbacks, we formulate and solve the problem of designing such a switching scheme as a constrained optimization problem with the objective of maximizing an estimate of the domain of attraction. Simulation results indicate that the resulting domain of attraction extends well beyond the linear regions of the actuators. View full abstract»

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  • Parallel Optimal Control for Weakly Coupled Nonlinear Systems Using Successive Galerkin Approximation

    Publication Year: 2008 , Page(s): 1542 - 1547
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    This technical note presents a new algorithm for the closed-loop parallel optimal control of weakly coupled nonlinear systems with respect to performance criteria using the successive Galerkin approximation (SGA). By using the weak coupling theory, the optimal control law can be obtained from two reduced-order optimal control problems in parallel, but the resulting problem is difficult to solve for nonlinear systems. In order to overcome the difficulties inherent in the nonlinear optimal control problem, the parallel optimal control laws are constructed in terms of the approximated solutions to two independent Hamilton-Jacobi-Bellman equations using the SGA method. One of the purposes of this note is to design the closed-loop parallel optimal control law for the weakly coupled nonlinear systems using the SGA method. The second is to reduce the computational complexity when the SGA method is applied to the high-order weakly coupled systems. View full abstract»

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Aims & Scope

In the IEEE Transactions on Automatic Control, the IEEE Control Systems Society publishes high-quality papers on the theory, design, and applications of control engineering.  Two types of contributions are regularly considered

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Meet Our Editors

Editor-in-Chief
P. J. Antsaklis
Dept. Electrical Engineering
University of Notre Dame