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In this communication three applications where the use of chaos improves the device are dealt with. The first application concerns the use of chaos to drive sonar sensors in multi-user scenarios. The second application deals with the use of chaos to enhance motion control of a microrobot. The third application deals with a new synchronization scheme for chaotic systems.

The interplay of noise and nonlinearity often leads to novel phenomena in micro- and nano-systems. Such phenomena are of fundamental and practical interest since they have the potential to offer new functionalities and to improve the performance of sensors. For instance, nonlinear systems often develops bistability when the periodic driving is sufficiently strong. In the presence of fluctuations, the nonlinear system can be induced to escape from one metastable dynamical state into the other. Unlike equilibrium systems where the escape rate can be calculated from the height of the free-energy barrier [1], driven systems are, generally, far from thermal equilibrium and cannot be characterized by free energy [2–5]. Consequently, the escape rate in such non-equilibrium systems must be derived from system dynamics [6–9]. Experiments on noise induced switching has been performed in a number of driven nonlinear systems, including parametrically driven electrons in a Penning trap [10], doubly clamped nanomechanical beams [11, 12] and radio frequency driven Josephson junctions [13]. Calculation of the escape rate in such non-equilibrium systems is a non-trivial problem and has attracted much interest [7, 8, 14, 15].

Experiments on noise-induced escape of a mesoscopic particle in a double-well potential are described. The potential is created by the interaction of two focused laser beams with a single sub-micrometer dielectric particle. By mapping the 3-dimensional trapping potential, the eigenfrequencies of the trapped particle are found. Over-barrier transitions are directly measured as a function of the rate and amplitude of a modulation that periodically tilts the potential. At low modulation rates and amplitudes the particle follows the potential adiabatically. As the system approaches its saddle-node bifurcation, different scaling regions emerge, each characterized by distinctive power-laws as predicted by recent theories. Of particular interest is the presence of a weakly non-adiabatic region with novel critical behavior.

Bestriding the realms of classical and quantum mechanics, nanomechanical structures offer great promise for a huge variety of applications, from computer memory elements [1] and ultra-fast sensors to quantum computing. Intriguing as these possibilities are, there still remain many important hurdles to overcome before nanomechanical structures approach anything close to their full potential. With their high surface-to-volume ratios and sub-micron dimensions, nanomechanical structures are strongly affected by processing irregularities and susceptible to nonlinear effects. There are several ways of dealing with nonlinearity: exceptional fabrication process control in order to minimize the onset of nonlinear effects or taking advantage of the interesting and oftentimes counterintuitive consequences of nonlinearity.

The paper reports on theoretical and experimental results related to the thermal control of microactuators based on shape memory alloy thin films. The behaviour of actuators that have one or more phase transforming films deposited on a non-transforming substrate is influenced by the thermal stress that grows in the bimorph or trimorph architecture on cooling from the deposition or annealing temperature. When a phase transition occurs or is induced in the film it leads to a corresponding change in the stress state in the film/substrate architecture and can be reflected accordingly in the actuation of a cantilever. The hysteretic characteristics of the actuation by shape memory alloy films can be controlled by appropriately selecting the chemical composition of the film, the substrate material, the film/substrate thickness ratio and in some cases the external stimuli. The deposition temperature was a factor considered for modulating the output signal of the bimorph and trimorph cantilevers, as well as the sequence(s) of deposition in case of multilayers and trimorphs. Bimorphs with bilayer and structurally graded films and trimorph architectures have been characterized based on known results for bimophs with single layer deposited on the same type of Si cantilever-type substrates. The results show how the martensitic transformation occurring in the films or in the layers or microlayers is affecting the response of the actuator to thermal stimuli. The models proposed could allow the selection of appropriate parameters in order to generate a specific type of actuation or a modulated sensorial response to thermal (for shape memory alloy) or thermal and magnetic (for ferromagnetic shape memory alloy) stimuli.

Overdamped bistable dynamics, of the generic form = –∇(), underpin the behavior of numerous systems in the physical world. The most-studied example is the overdamped Duffing system, the dynamics of a particle in a bistable potential () = – + . Absent an external forcing term, the state-point () will rapidly relax to one of two stable attractors, for any choice of initial condition. It has been shown [1], however, that coupling similar elements via a linear uni-directional coupling with cyclic boundary conditions, can lead to oscillatory behavior past a critical value of the coupling coefficient. Typically, this behavior is dictated by symmetry conditions [2], and is generated via Hopf bifurcations; it appears to occur in any coupled system of overdamped bistable elements, none of which would oscillate when isolated and undriven, subject to the appropriate choice of parameters and operating conditions (albeit through different bifurcation mechanisms).

Ionic Polymer Metal Composites or IPMCs are innovative materials, light and soft, that show very interesting electromechanical properties to be used in several fields of research, such as robotics, measurements, biomedics. In this paper details on IPMCs will be given: from their state of the art to their modeling and characterization; tools and equipments, designed and realized to perform measurements on the IPMCs will be presented.

Interacting, multi-robot systems show increasing promise for advances in exploration and defense applications. Here, we model a non-linear system of self-propelled individuals interacting via a pairwise attractive and repulsive potential. Depending on the interaction parameters, the agents may disperse, accumulate into self-organizing structures such as flocks and vortices, or collapse onto themselves. Borrowing tools from Statistical Mechanics, we discuss the connections between the H-stable nature of the interaction potential and resulting aggregating patterns and asymptotic behaviors.

Models and theoretical findings of Residence Times Di.erence (RTD) Fluxgate have been already presented in previous papers. A very simple sensor structure, negligible onboard power requirements and the intrinsic digital form of the readout signal are the main features of the proposed strategy. In this paper we aim to investigate main sources of uncertainty, including noise, and possible strategies to limit their effects on the devices; finally results on noise characterization are presented.

Novel inertial sensor based on ferrofluids are presented in this paper. The proposed devices have a widely tunable operative range and high sensitivity. A ferrofluidic sample in aqueous suspension acts as inertial mass. The devices are constituted by one excitation coils and one differential sensing coil wound around a glass pipe where the ferrofluid is contained. The bias magnetic force, induced by the coil, attracts the ferrofluid in its centre thus acting like an equivalent spring. The acceleration to be measured reflects therefore in the inertial mass oscillation amplitudes that are sensed by using a differential transformer whose output voltage is a function of the ferrofluid position. Analytical models, simulations and experimental result are presented to demonstrate the suitability of the proposed approach.