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Shape memory alloys (SMA) are excellent candidates for implementation in actuator systems due to their ability to recover their original shape after high-strain loading through a thermally-induced phase transition. In this work, we propose and develop a novel SMA-metamaterial actuator which is capable of exhibiting a reversible, global elongation in multiple directions induced by the unidirectional contraction upon heating of a single SMA component. This actuator consists of (a) an SMA component, (b) a bias component and (c) the metamaterial geometry, with each component having a distinct function: (a) actuation activation, (b) reversibility of actuation upon deactivation and (c) amplifying and re-directing the uni-directional SMA actuation globally throughout the actuator, respectively. A prototype actuator was designed and tested in various configurations over multiple activation/deactivation cycles in order to demonstrate the functionality and reusability of this system. Furthermore, a theoretical model which predicts the actuation stroke of the system on the basis of the material properties of the SMA and bias components as well as the geometry of the metamaterial system was developed and validated. The findings of this work demonstrate the considerable potential of SMA-metamaterial actuators for implementation in systems requiring a multi-axial actuation output.

Shape memory alloy (SMA)-based actuator composites are characterised by a high force output which is activated by a temperature increase. In this work we exploit this property to design sandwich structures with SMA-matrix composite actuator skins capable of exhibiting a reversible, tailored flexural response. A theoretical model which predicts the resultant deflection and flexural moment produced as a result of selectively actuating one of the system skins was developed and confirmed using a multi-step Finite Element (FE) analysis which takes into account the fabrication pathway through which these systems may be manufactured. The model correlates the geometric parameters and material properties of the various components making up the system and provides a quantitative description of the role which each variable plays in determining the overall sandwich actuator performance. This is necessary for the future production and implementation of such systems in real-life applications.

The direct elastomagnetic effect in composite materials, made of ferromagnetic micro-magnets inside an elastomeric matrix, consists in their relative elastic deformation (10-4-10-3) under the action of an external magnetic field, dependent on the equilibrium between the magneto-mechanical moments and the internal elastic reaction, but independent of the standard magnetostriction. This investigation is focused on the evaluation of the strain linearity with the excitation field in view of the application of these materials for MEMS devices. The studied composite is made of permanently magnetized Sm2Co7 microparticles uniformly dispersed inside a silicone matrix. The field-induced strain is measured using a fiber Bragg grating sensor and, at the same time, theoretically evaluated from the model of the direct elastomagnetic effect. The linearity and reversibility of the material response are experimentally verified up to a threshold value of the magnetic field corresponding to the break in the coupling between the particles' magnetic moments and their body and to the passage from the linear magnetization to the non-linear regime accompanied by irreversible magnetization processes.

This paper presents the design and the experimental implementation of fast and periodic output feedback controllers to minimize structural vibration, using collocated piezoelectric actuators and sensors. A linear dynamic model of the smart cantilever beam is obtained using online recursive least squares parameter estimation. A digital control system that consists of simulink modeling software and a dSPACE1104 controller board has been used for identification and control. The effectiveness of the controllers is shown experimentally by exciting the structure at resonance.

The deflection and time response of shape memory alloy laminated composite plate are studied using first order shear deformation theory. The composite plate consists of a thin layer of shape memory alloy bonded to an elastomer layer. The governing equations of the plate are developed using the energy balance equations and a two-dimensional model of the shape memory alloy layer. The finite element is modeled with the first order shear deformation theory and equivalent single layer assumptions. The model is validated by comparing the results of the displacements and time responses with the literature. As a specific example, a cantilever composite plate is used for parametric studies. The effect of material properties, electric input power, thickness, thermal conductivity and heat sink strength on deflection and time response is also investigated.

This paper presents a new velocity sensor whose output is directly proportional to velocity at low frequencies, but has a well damped resonance after which it has a controlled roll-off. It is designed to be used in a feedback loop with a closely located piezoelectric patch actuator to form a sensor–actuator pair for the implementation of active damping. The velocity sensor consists of a principal spring–mass seismic sensor with an internal direct velocity feedback control loop. This internal feedback loop uses a separate control spring–mass seismic sensor and a reactive actuator, which are fixed on the seismic mass of the principal sensor. The control gain is tuned to obtain two effects: first, the output signal from the principal sensor becomes directly proportional to the velocity at the base of the sensor itself and second, the fundamental resonance peak is reduced by the active damping effect of the internal feedback loop. The practical feasibility is then studied by considering a prototype model. The stability of the internal feedback control loop has been assessed first, following which the frequency response function of the sensor with and without the internal feedback loop has been measured. The experimental measurements have shown that the internal feedback loop is conditionally stable but guarantees sufficient gain margins to obtain the desired velocity output from the sensor. The sensor has been successfully tested with a closed loop, and shows the desired velocity output with no resonance at the fundamental natural frequency of the seismic sensor.

Effective elastic, actuation, thermal expansion and hygroscopic expansion coefficients for periodic smart composite structures are derived through the application of asymptotic homogenization models. The actuation coefficients characterize the intrinsic transducer nature of active smart materials that can be used to induce strains and stresses in a controlled manner. The pertinent mathematical framework is that of asymptotic homogenization. Differential equations with rapidly oscillating coefficients which govern the behavior of a general anisotropic (composite) material with a regular array of reinforcements and/or actuators are transformed into simpler ones that are characterized by some effective coefficients; it is implicit, of course, that the physical problem based on these effective coefficients should give predictions differing as little as possible from those of the original problem. The governing equations pertaining to a generalized model of a smart structure with non-homogeneous boundary conditions are derived and are shown to differ from those of a corresponding problem with homogeneous boundary conditions by what amounts to a boundary layer solution. The effective properties are determined by means of so-called `unit cell' problems and calculated for the case of periodic laminates. The use of these effective coefficients is illustrated by means of two- and three-dimensional examples.

In this paper, a methodology to control the surface error on a Doppler antenna using the concept of a variable geometry truss structure is proposed. A genetic algorithm is used to find the optimal location and number of actuators with the objective to minimize the construction and runtime costs. The optimization also takes into account the limitations in actuation. A piezoceramic-based actuator is used to demonstrate the effectiveness of the methodology. A simple illustration of 2D trusses, which could form a part of a Doppler antenna structure, is used to show the efficacy of the method. An analysis of the effectiveness of such a design is presented. The influence of the variables in the problem is examined and observations made. This study concludes that the smart antenna concept is a viable, feasible and effective option in design.

Smart/intelligent/adaptive structures with distributed, integrated sensors, actuators and control electronics are being investigated extensively for possible use in high-performance, light-weight structural systems. Due to the unique electromechanical coupling, these piezoelectric materials could be used as sensors and actuators in smart structures. This work deals with the active vibration control of smart/intelligent shells with a distributed piezoelectric sensor and actuator layer bonded onto the top and bottom surfaces of the structures. A shear-flexible nine-noded shell finite element derived from the field consistency approach has been used for the investigation. This element has been developed so as to have one electrical degree of freedom per piezoelectric layer per element. The mass, stiffness and electromechanical coupling effects of the piezoelectric sensor and actuator layer are considered. The control performance with different types of loading is investigated. A linear quadratic regulator optimal control scheme is used to obtain the control gains.

The programmable sequential actuation of two-dimensional hydrogel membranes into three-dimensional folded architectures has been achieved by combining ionoprinting and redox chemistry; this methodology permits the programmed evolution of complex architectures triggered through localized out-of-plane deformations. In our study we describe a soft actuator which utilizes ionoprinting of iron and vanadium, with the selective reduction of iron through a mild reducing agent, to achieve chemically controlled sequential folding. Through the optimization of solvent polarity and ionoprinting variables (voltage, duration and anode composition), we have shown how the actuation pathways, rate-of-movement and magnitude of angular rotation can be controlled for the design of a 4D sequential actuator.

This experimental study investigates the coupled effect of the force developed by the shape memory alloy (SMA) actuators and the force required for the large deflection of an elastica member in a compliant parallel mechanism. The compliant mechanism developed in house consists of a moving platform mounted on a superelastic pillar and three SMA wire actuators to manipulate the platform. A three-axis MEMS accelerometer has been mounted on the moving platform to measure its tilt angle. Three miniature force sensors have been designed and fabricated out of cantilever beams, each mounted with a pair of strain gauges, to measure the force developed by the respective actuators. The force sensors are highly sensitive and cost effective compared to commercially available miniature force sensors. Calibration of the force sensors has been accomplished with known weights, and for the three-axis MEMS accelerometer a rotary base has been considered which is usually used in optical applications. The calibration curves obtained, with R-squared values between 0.9997 and 1.0, show that both the tilt and force sensors considered are most appropriate for the respective applications. The mechanism fixed with the sensors and the drivers for the SMA actuators is integrated with a National Instrument's data acquisition system. The experimental results have been compared with the analytical results and it was found that the relative error is less than 2%. This is a preliminary study in the development of a mechanism for eye prosthesis and similar applications. � 2008 IOP Publishing Ltd.

This paper deals with the formulation of a nine-noded piezolaminated degenerated shell finite element for modeling and analysis of multilayer composite general shell structures with bonded/embedded distributed piezoelectric sensors and actuators. The distributed PZT sensors and actuators used in the composite smart structures are relatively thin and could have arbitrary variation of curvatures and thicknesses. They cannot be modeled with shell elements based on curvilinear shell theories which would need the specification of constant shell curvatures and thicknesses. Modeling them with piezo finite elements available in popular commercial codes like ABAQUS, ANSYS, MARC, etc, would need relatively greater computational effort as they are based on solid element formulation. In view of these, the present proposed degenerated piezoelectric shell element would be a better choice giving good computational accuracy and efficiency. The main advantage of a degenerate shell element is that it is not based on any shell theories and is applicable over a wide range of curvatures and thicknesses. This element is developed by using the degenerate solid approach based on Reissner-Mindlin assumptions which allow the shear deformation and rotary inertia effect to be considered and the 3D field is reduced to a 2D field in terms of mid-surface nodal variables. Uniformly reduced integration is carried out to overcome membrane locking and shear locking and the numerical integration is carried out in all three directions to obtain accurate results. The present element has 45 elastic degrees of freedom and 10 electric degrees of freedom per piezoelectric layer in the element. The potential induced due to bending deformation is more accurately represented by assuming quadratic variation of the electric potential through the thickness of each piezoelectric layer. This is achieved by interpolating using nodal mid-plane electric potentials and one electric degree of freedom representing the potential difference between the top and bottom surfaces of the piezoelectric layer. Few case studies of composite general shells with piezoelectric sensors and actuators have been considered by modeling them with the above elements and the active vibration control performance has been studied using linear quadratic Gaussian (LQG) control. � 2008 IOP Publishing Ltd.