A vibrational energy harvester based on soft-nonlinearity for truly random excitation

Abstract In this paper, we present a nonlinear energy harvester that is based on a “soft-mode” nonlinearity and is able to work in presence of a truly random excitations. The proposed harvester is configured with a cantilever beam structure, and, at the tip is a cylindrical container filled with freely moving iron balls. The nonlinearity is implemented through the container, as a piecewise function. This structure, in presence of noise, can be assumed as a second order (mass-spring-damper) nonlinear system where the length of the spring changes as a function of external vibration. As will be demonstrated, this nonlinearity will improve the performance of the energy harvester under random excitation. In comparison, the conventional approach based on resonant oscillators is able to collect energy only around its mechanical natural frequency, while the solution pursued here will present a wide spectrum of response. Furthermore, the implemented nonlinearity here does not possess any barrier of potential or mechanical threshold. Because of this, it is able to work at weak signal levels and without mixture of periodic signals. A piezoelectric element has been used to convert the mechanical vibrations into an electrical signal. The system has been modeled and simulated. Experimental validations have been carried out, demonstrating the suitability of the proposed solution

Exploiting Nonlinear Dynamics in Novel Measurement Strategies and Devices: From Theory to Experiments and Applications

International audienceThis paper is focused on the exploitation of intrinsic nonlinear dynamics toward novel measurement systems and readout methodologies. In particular, sensors that can be represented as nonlinear dynamical systems and are often reducible to systems described by a static nonlinearity are considered; the nonlinear behavior therefore reduces to the dynamics of a system characterized by two or more (meta)stable equilibrium states (or attractors) separated by energetic thresholds to be overcome to transition from one attractor to the other. The presence of a weak unknown target signal is assessed via the monitoring of the "residence times" in the attractors. This operational scenario that is based on the monitoring of suitable "events" avoids an "amplitude-based" readout and provides a very simple and sensitive readoutprocessing scheme. Many noise effects are also mitigated by the intrinsic decoupling between the amplitude domain of the input signal and the event or time domain of the output signal. We present here the general transduction methodology for this class of "residence-times difference" sensors, together with the experimental results obtained from the working versions of these sensors (in particular, a simple fluxgatemagnetometer).We then introduce some novel dynamical behavior that occurs when the active nonlinear (in this case, bistable) elements are coupled using well-crafted coupling topologies. Sensors based on these coupling schemes provide several advantages over their single-element counterparts. We discuss the dynamics of the coupled-element device, summarizing recent theoretical and experimental results. Finally, we describe the construction and performance of working devices (magnetic- and electric-field sensors) based on these concepts