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This quantitative study examined student participation in an introductory project-based engineering course offered in fully face-to-face and hybrid course modes (N = 160). This course attempted to counteract trends of decreased student motivation and high attrition rates among engineering majors. Mixed-design analysis of variance examined differences in motivational constructs including student self-efficacy, effort regulation, and interest in engineering, as well as engineering skills throughout the course and across instructional modes. None of the motivational constructs were associated with significant decreases throughout the course nor with differences across instructional modes. However, students' engineering skills increased throughout the course with no significant differences across course modalities. Furthermore, interest in engineering and effort regulation were positively associated with course performance. The instructional modality was not significantly associated with course performance. Overall, this study provides an example of a project-based introductory engineering course which may help maintain student motivation and foster student success in engineering.

A synthesis technique based on a mechanical finite-element (FEM) surface description of dual-offset reflector (DOSR) surfaces is described. This technique is used to implement a reconfigurable contour beam for a geostationary satellite application. The mechanical finite-element description of the surface takes into account the mechanical properties of the reflector surfaces and the effect of a finite number of forces applied at control points on the surface. Mechanical adjustment is achieved using high-deflection stacked piezoelectric actuators attached to the rear of a lightweight flexible subreflector surface. Both the main and sub-reflector surfaces are shaped for an initial required geographical coverage zone and then the main reflector surface is assumed to be fixed in shape. The variable shape subreflector is then synthesized to achieve the desired illumination for different geographical regions and different geostationary positions. Based on a study of the effect of the mechanical properties of the subreflector surface and actuator number and placement, a practical design has been completed and the ability to reconfigure the beam has been verified. Index Terms--Adjustable surface, reconfigurable contour beam, reflector antenna.

Photoelectrochemical (PEC) etching is a rapid and inexpensive means of etching GaN, InGaN, and related materials for micro-electro-mechanical systems (MEMS) applications. In this work, we show that bandgap engineering of GaN/InGaN heterostructures can be used to exert substantial control over PEC etching and achieve strain-free cantilevers. A single, 200-nm thick layer InGaN was selectively etched using bandgap-selective PEC etch. We show that the use of highly doped guard layers to confine photogenerated holes uniformly across the InGaN layer enables a uniform, fast, and effective PEC etch. This approach enables complete uniform etching using PEC and could enable many optical and MEMS devices. [ABSTRACT FROM AUTHOR]

Curved piezoceramic unimorph actuators exhibit strong nonlinearities due to their special architecture that enables large motion amplification. Among these nonlinearities, hysteresis is the most problematic as it makes it difficult to predict the displacement of the actuator for a given input voltage. Therefore, it has been difficult to use these actuators in precision displacement control applications. In order to overcome this difficulty, this research is focused on the development of an effective reference-tracking displacement control algorithm for such actuators. For this purpose, two linear (proportional–integral and internal model) and two nonlinear (sliding mode and model predictive sliding mode) controllers are designed and implemented. These controllers are applied to the curved piezoceramic unimorph actuator to control the displacement of the actuator for multiple sinusoidal voltage inputs at various frequencies. Experimental results are obtained, and their performance is compared both qualitatively and quantitatively. As a part of the model-based controller design, a new actuator model is also developed based on the mechanical second-order equation with an additional phase lag term to describe the hysteretic effect. [ABSTRACT FROM AUTHOR]

This article focuses on the active control of a combination of incommensurate sinusoids and its subsets. Two sliding mode control (SMC) algorithms are proposed to enhance the conventional least mean squares (LMS) algorithm maintaining its inherent advantages. The SMC is utilized to update the filter coefficients, and a feedback loop with the SMC is introduced in the adaptive filtering system. The proposed methods are evaluated for several cases by comparing the results with the LMS algorithm. An experiment with an active strut is also constructed and longitudinal vibrations excited by an amplitude modulated type signal are measured before and after the control for each adaptive filtering algorithm. Overall, the proposed algorithms demonstrate faster convergence and reduce amplitudes at multiple peaks even when only one frequency is targeted. [ABSTRACT FROM PUBLISHER]

This paper investigates application of a control algorithm called model predictive sliding mode control (MPSMC) to active vibration suppression of a cantilevered aluminum beam. MPSMC is a relatively new control algorithm where model predictive control is employed to enhance sliding mode control by enforcing the system to reach the sliding surface in an optimal manner. In previous studies, it was shown that MPSMC can be applied to reduce hysteretic effects of piezoelectric actuators in dynamic displacement tracking applications. In the current study, a cantilevered beam with unknown mass distribution is selected as an experimental test bed in order to verify the robustness of MPSMC in active vibration control applications. Experimental results show that MPSMC can reduce vibration of an aluminum cantilevered beam at least by 29% regardless of modified mass distribution. [ABSTRACT FROM AUTHOR]

The utilization of gallium nitride (GaN) in the area of microelectronics continues to increase due to the advantages it offers over other semiconductors. This paper presents GaN as a candidate material well suited for novel microelectromechanical systems (MEMS). The potential of GaN for MEMS is demonstrated via the design, analysis, fabrication, testing and characterization of an optical microswitch device actuated by piezoelectric and electrostrictive means. The piezoelectric and electrostrictive properties of GaN and its differences from common piezoelectrics are briefly discussed before touching upon the device configuration used to implement the microswitch device. Subsequently, the development of two recent fabrication technologies, photoelectrochemical etching and bias-enabled dark electrochemical etching, used to realize the three-dimensional device structure in GaN are described in detail. Lastly, an ultra-low-cost, laser-based, non-contact approach to test and characterize the microswitch device is described, followed by the device testing results. [ABSTRACT FROM AUTHOR]

Currently, piezoelectric actuators are being used in many applications from precision positioning control to active vibration control of large space structures. They can take the form of a solid-state device and are conveniently controlled by a voltage input. In spite of their relative ease of control, positioning accuracy and actuator longevity can be compromised by the hysteresis. Thus, the primary objective of this research is to minimize the hysteretic effect of a piezoelectric actuator in order to obtain a near linear relationship between the input voltage and the output displacement. The reduction of the hysteresis is accomplished by a newly developed control methodology named model predictive sliding mode control. A nonlinear energy-based hysteresis model is developed for a piezoelectric stack actuator and model predictive sliding mode control is applied to force the system state to reach a sliding surface in an optimal manner and track the reference signal accurately thereafter. To validate this new approach, simulations and experiments are conducted and the results highlight significantly improved hysteresis reduction in the displacement control of the piezoelectric stack actuator. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the control design problem associated with the use of an electrically assisted turbo-charger (TC) for a modern Diesel engine plant. It is shown that the proposed system has the potential of improving the control bandwidth of air charge regulation relative to conventional systems. The improved control authority creates the potential for precise regulation of the fresh air fraction in the air charge. A previously developed model of a Diesel engine with variable geometry turbocharging (VGT) and Exhaust Gas Recirculation (EGR) is augmented with the model of a permanent magnet synchronous motor (PMSM) to create the model of the Turbo Electrical Assist (TEA) system. The effect of exhaust gas recirculation (EGR) on the electric power requirement of the PMSM is examined over a federal test procedure (FTP) test drive cycle. Control design is performed using the sliding mode framework. [ABSTRACT FROM AUTHOR]

In this study, the authors develop haptic systems for telerobotic surgery exploiting MR fluids for semiactive force feedback. To investigate the full range of tactile force exhibited by a particular MR damper design, a microstructural 3D kinetic theory-based model of MR fluids has been developed. In this model, microscale constitutive equations relate flow, stress, and particle orientation. The higher accuracy of the model in this regard gives better force representations of highly compliant objects. In this article, the model is utilized in forcefeedback control of both a SDOF system and a 2DOF system. A state-feedback control algorithm is employed to track both the SDOF system, and the 2DOF system using specially designed MR force-feedback joysticks. The results demonstrate that the MR fluid-based forcefeedback joysticks can be used effectively as haptic devices. It is also observed that both SDOF and 2DOF systems are nearly transparent in replicating the stiffness of different external objects, due to the light weight of the semiactive system and controller implementation. [ABSTRACT FROM AUTHOR]

High bandwidth actuation systems that are capable of simultaneously producing relatively large forces and displacements are required for use in automobiles and other industrial applications. Conventional hydraulic actuation mechanisms used in automotive brakes and clutches are complex, inefficient and have poor control robustness. These lead to reduced fuel economy, controllability issues and other disadvantages. Recently, a two-stage hybrid actuation mechanism was proposed by combining classical electromechanical actuators like DC motors and advanced smart material devices like piezoelectric actuators. This article discusses the development and implementation of a model predictive control methodology for controlling this two-stage actuation system in tracking various reference inputs. Additionally, this methodology also employs a unit-step delayed disturbance estimate to account for actuator hysteresis, other nonlinearities and unmodeled dynamics in the system. Finally, the article highlights the effectiveness of this control methodology experimentally by tracking various reference inputs. [ABSTRACT FROM AUTHOR]

Prior experimental measurements by the authors demonstrated large reversible strains of -0.41% along the [001] crystal direction of a cylindrical Ni50Mn28.7Ga21.3 rod driven with a magnetic field along the same direction and no external restoring force. The origin of the reversibility is attributed to internal bias stresses generated by impurities absorbed during manufacture of the alloy. This article presents a macroscopic constitutive model for Ni-Mn-Ga strain in collinear field and stress configuration. The switching between two variant orientations in the presence of Zeeman energy and the pinning energy of the impurities is formulated through a Gibbs energy function for the crystal lattice. Inhomogeneous local interaction fields and impurity distributions are addressed through stochastic homogenization techniques. Attributes of the model are illustrated through comparison of model results with strain-field measurements collected at various compressive loads. Constrained optimization is used to determine the necessary parameters and an error analysis is performed to assess the accuracy of the model for various loading conditions. The collinear field and stress configuration can lead to solenoid transducers with enhanced energy density and bandwidth relative to standard electromagnet devices. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) dampers are easily controlled by appropriately regulating the current through an electromagnet producing the necessary magnetic field across the fluid; thus they can be utilized in applying advanced nonlinear control strategies aimed at vibration suppression problems. Since most MR dampers are passive (i.e., they are dissipative and do not produce motion) modern nonlinear control schemes must be significantly modified before they can be employed. This study presents the theoretical development of a modified nonlinear control methodology for MR dampers applied to typical vibration control problems. The methodology is applied to single and multiple DOF systems. The case when only one measurement sensor is used in a quarter-car model is also analyzed using a classical observer design. Simulated and experimental results show the effectiveness of the methodology in controlling the vibration of a general vibratory system. [ABSTRACT FROM AUTHOR]

Ferromagnetic shape memory Ni-Mn-Ga has been shown to exhibit deformations of up to 9.5% when driven with quasistatic fields. This article is focused on the use of Ni-Mn-Ga as the active element in a dynamic transducer consisting of a solenoid and a low-reluctance, closed magnetic path. Despite the absence of a restoring force in this configuration, we have shown in prior studies recoverable compressible strains of λ= -4100 μϵ, which are attributable to internal bias stresses built in the material during manufacture. In this study, we experimentally establish the presence of a modulus defect in Ni50Mn28.7Ga21.3, whereby the elastic modulus increases as much as 255% upon increasing the applied magnetic field from zero to 380 kA/m DC. Experimental measurements are conducted under both mechanical and magnetic excitation, and analyzed in combination with vibratory models for the system. While in our experiments the attractive magnetic forces between the transducer poles may contribute to the total modulus increase, the presence of a modulus change associated with the Ni-Mn-Ga element is substantiated. Dynamic Ni-Mn-Ga transducers offer an attractive mechanism for electrical tuning of the modulus, with potential application in active vibration absorption problems. [ABSTRACT FROM AUTHOR]

Conventional shear mode transmission clutches using magnetorheological fluids (MRFs) can be either disc-shaped or cylindrical. The major drawbacks of these devices include the effect of centrifuging at high rotational speeds and the subsequent sealing problems associated with it. This study develops models aimed at describing centrifuging and mitigates this issue by developing a MR clutch design where the fluid is encapsulated in a highly absorbent polyurethane foam. [ABSTRACT FROM AUTHOR]

In this research, an antenna's far field radiation pattern is controlled by controlling the shape of a sub reflector in a Cassegrain antenna system. The antenna is actuated using multiple point actuators in contact with the reflector surface. A lead zircamate titanate (PZT) stack coupled with a friction-based compliant mechanism gives the point actuators used in this design an advantage over similar studies using PZT bimorph or PVDF actuators. The main advantage stems from the fact that the displacement can be maintained without the continuous application of voltage. An electromechanical model is used to describe the motion of the stack, and the friction based compliant mechanism is modeled similar to power screw-type actuators. A combined finite element-electromagnetic analysis code is used to determine the desired shape of the reflector and the corresponding actuator displacements. The final shape of the reflector is verified using stereo photogrammetry. [ABSTRACT FROM AUTHOR]

A synthesis technique and mechanical design for a reconfigurable contour beam dual-offset-reflector antenna for satellite application are described. Mechanical adjustment is achieved by attaching high-deflection stacked piezoelectric actuators to the rear of a lightweight flexible subreflector surface. Both the main and subreflector surfaces are shaped for an initial required geographical coverage, and the main reflector surface is then assumed to have a fixed shape. The variable shape subreflector is then synthesized to achieve required coverage for different geographical regions and different geostationary positions. To develop this system, the following methodology was developed. Based on the required subreflector surface displacement, mechanical finite-element analysis was conducted on the reflector surface, and an actuator placement study was completed. The surface deflections attained from mechanical actuation were then compared to the required surface deflections. The achieved subreflector surface error was calculated, as well as the effect of the error on the radiation pattern. The results show that one can achieve acceptable performance from a finite amount of actuators on a reflector surface. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 436–446, 1999. [ABSTRACT FROM AUTHOR]