[en] The electromagnetic acoustic transducers (EMATs) are gaining much attention in recent years due to their non-contact operation in ultrasonic wave generation and reception in NDT field. Quite often the transduction efficiency of EMATs is low, so efforts are always necessary to gain a better understanding of their complex and multi-physics transduction mechanism. In this work, we focused on modeling of an omni-directional Lorentz force-based EMAT operating on an aluminum disk and containing a rounded meander coil to generate a pure Lamb wave mode. We introduced an approach to solve the underlying eddy current equations in cylindrical coordinates directly, and applied this approach to a multi-conductor electromagnetic model to investigate the skin and proximity effects. These effects existed both for the complete and incomplete equations. Then we built the omni-directional EMAT model composed of three sub-models and two geometries. The two-geometry structure made it possible to reduce the total number of elements. Time varying spatial distribution of the Lorentz force vector was plotted. Propagation velocity of the simulated wave packet was compared with the group velocity of desired S0 mode Lamb waves. Interaction of the waves with a slot defect with a depth of 50% thickness was studied. The response to high current excitation and dynamic magnetic field was also investigated. (paper)

[en] Pyroelectric materials have recently received attention for harvesting waste heat owing to their potential to convert temperature fluctuations into useful electrical energy. One of the main challenges in designing pyroelectric energy harvesters is to provide a means to induce a temporal heat variation in a pyroelectric material autonomously from a steady heat source. To address this issue, we propose a new form of wind-driven pyroelectric energy harvester, in which a propeller is set in rotational motion by an incoming wind stream. The speed of the propeller’s shaft is reduced by a gearbox to drive a slider-crank mechanism, in which a pyroelectric material is placed on the slider. Thermal cycling is obtained as the reciprocating slider moves the pyroelectric material across alternative hot and cold zones created by a stationary heat lamp and ambient temperature, respectively. The open-circuit voltage and closed-circuit current are investigated in the time domain at various wind speeds. The device was experimentally tested under wind speeds ranging from 1.1 to 1.6 m s⁻¹ and charged an external 100 nF capacitor through a signal conditioning circuit to demonstrate its effectiveness for energy harvesting. Unlike conventional wind turbines, the energy harvested by the pyroelectric material is decoupled from the wind flow and no mechanical power is drawn from the transmission; hence the system can operate at low wind speeds (<2 m s⁻¹). (paper)

[en] Due to the controllability of the stiffness and damping under the applied magnetic field, magnetorheological elastomer isolator has been proved effective in the field of vibration control. For the realization of vibration control application, an accurate MRE isolator model is a non-trivial task. However, the existing parametric modeling methods are required to identify too many parameters, which are difficult to implement. Moreover, the corresponding inverse dynamic model of the isolator cannot even be obtained by the identified model inversion. Therefore, this paper proposes a nonparametric neural network approach to approximate the dynamic behaviors of magnetorheological elastomer isolator with the characteristics of nonlinearity and hysteresis. Firstly, the dynamic characteristics of the isolator in shear-compression mixed mode are experimentally tested under different loading conditions. Secondly, based on the experimental data, a NARX neural network with three-layer structure is developed to approximate the functional relationship between inputs (displacement, velocity and current) and output (force) of magnetorheological elastomer isolator. Thirdly, the effectiveness of the network model is validated by comparing the predicted force and experimental force. Finally, considering the common occurrence of inputs with noise disturbance in real application, the robustness of the network is also verified for displacement and current inputs with noise disturbance, respectively. The results of the network generalization for experimental data show that the proposed NARX network is more robust and optimal than BP network. (paper)

[en] In our work we present the complete development process of geometrically complex micro-vascular shape-memory polymer actuators. The complex geometries and three-dimensional networks are designed by means of computer aided design resources. Manufacture is accomplished, in a single step, by means of laser stereolithography, directly from the computer-aided design files with the three dimensional geometries of the different actuators under development. To our knowledge, laser stereolithography is applied here for the first time to the development of shape memory polymer devices with complex geometries and inner micro-vasculatures for their activation using a thermal fluid. Final testing of the developed actuators helps to validate the approach and to put forward some present challenges. (paper)

[en] In this paper, a new piezo-actuated XY parallel compliant mechanism for large workspace nano-positioning with decoupled motions is developed by incorporating a novel Z-shaped flexure hinge (ZFH)-based mechanism into the mirror-symmetrically distributed structure. The bridge-type mechanism and two-stage leverage mechanisms serve as preliminary displacement amplifiers, while further amplification with motion transfer and decoupled output motions are achieved by means of the ZFH mechanism. Based on finite element theory, a high-precision analytical model of the XY compliant mechanism is established by considering all the connecting linkages as flexible components. Through the improved differential evolution algorithm, the optimized compliant mechanism is capable of performing millimeter-scale workspace nano-positioning with decoupled motions. In addition, the input displacement unbalance, resulting from the lateral force which has potential to damage the piezoelectric actuators, is markedly lowered to a negligible value. The performance of the fabricated compliant mechanism with optimized parameters is investigated to well agree with both the analytical model and ANSYS simulation. In addition, based on the inverse kinematics derived from the model and experimental results, different elliptical vibration trajectories are accurately acquired. (paper)

[en] In this paper, a novel design of asymmetry bistability for a coupled dielectric elastomer minimum energy structure (DEMES) is presented. The structure can be stable both in the stretched and curved configurations, which are induced by the geometry coupling effect of two DEMESs with perpendicular bending axes. The unique asymmetry bistability and fully flexible compact design of the coupled DEMES can enrich the active morphing modes of the dielectric elastomer actuators. A theoretical model of the system’s strain energy is established to explain the bistability. Furthermore, a prototype is fabricated to verify the conceptual design. The experimental results show that when the applied voltage is below a critical transition one, the structure behaves as a conventional DEMES, once the applied voltage exceeds the critical voltage, the structure could change from the stretched (curved) configuration to the curved (stretched) configuration abruptly and maintain in a new stable configuration when the voltage is removed. A multi-segment structure with the coupled DEMES is also presented and fabricated, and it displays various voltage-actuated morphings. It indicates that the coupled DEMES and the multi-segment structures can be useful for the soft and shape-shifting robots. (paper)

[en] In the design of a laminated magneto-rheological elastomeric bearing (MREB), the passive rubbers are replaced with composite layers of rubber and MREs. The applied magnetic field, produced by the built-in electromagnet through the input current, changes the stiffness and damping of MREs, and thus that of the device. Typically, a good MREB should possess higher adjustable properties with less activating power in avoiding overheating problem. Thus an optimized design of MREB should integrate the MRE material design into mechanical and electromagnetic components to achieve a trade-off between power consumption and adjustability of stiffness. In this study, we propose a method to analyze and design a laminated MRE bearing, in which the optimal parameters of materials and mechanical structure of the MRE bearing are determined. Based on the multi-scale and magneto-mechanical coupling theories, we establish a multi-scale model for the MRE bearing considering the influence of particle volume fraction, particle distribution, and thickness of MRE laminated layers on its mechanical performance. Within the micro-scale analysis, the representative volume unit is used to address the effect of particle volume fraction and distribution on mechanical and magnetic properties of MRE itself. Within the macro-scale analysis, we build both mechanical and magnetic models for the laminated MRE bearing. Based on the theoretical analysis, a laminated MRE bearing with four-layer MRE is designed and fabricated. The performance of the MRE bearing has been tested by using MTS test bench. The results are compared with that of model analysis. Both experimental and theoretical results indicate that optimal design of MREB depends on the MRE’s particle volume fraction which is related with MREB’s input power limitation. (paper)

[en] This paper presents the development of a bimorph microelectromechanical system (MEMS) generator for vibration energy harvesting. The bimorph generator is in cantilever beam structure formed by laminating two lead zirconate titanate thick-film layers on both sides of a stainless steel substrate. Aiming to scavenge vibration energy efficiently from the environment and transform into useful electrical energy, the two piezoelectric layers on the device can be poled for serial and parallel connections to enhance the output voltage or output current respectively. In addition, a tungsten proof mass is bonded at the tip of the device to adjust the resonance frequency. The experimental result shows superior performance the generator. At the 0.5 g base excitation acceleration level, the devices pooled for serial connection and the device poled for parallel connection possess an open-circuit output voltage of 11.6 V_P–P and 20.1 V_P–P, respectively. The device poled for parallel connection reaches a maximum power output of 423 μ W and an output voltage of 15.2 V_P–P at an excitation frequency of 143.4 Hz and an externally applied based excitation acceleration of 1.5 g, whereas the device poled serial connection achieves a maximum power output of 413 μ W and an output voltage of 33.0 V_P–P at an excitation frequency of 140.8 Hz and an externally applied base excitation acceleration of 1.5 g. To demonstrate the feasibility of the MEMS generator for real applications, we finished the demonstration of a self-powered Bluetooth low energy wireless temperature sensor sending readings to a smartphone with only the power from the MEMS generator harvesting from vibration. (paper)

[en] In order to develop small loading and small damping, a small magneto-rheological fluid (MRF) damper with built-in magnetic coils is researched, and the dynamics model of new mini-damper is established based on testing the mechanical properties of the damper. It is found that the damping landing force adjustable range will be best when the damping gap is 1.5 mm. The loading force of the mini-damper is only 1.95 N–8.25 N by adjusting the coil current from 0 A–0.8 A. The smooth damping force is the third-order function with the current by polynomial fitting of the experimental data. The result of dynamics tests shows hysteresis damping characteristics, and an improved nonlinear dynamic model is proposed by combining with the structure characteristics. The parameters of the improved dynamic model are identified by using parameter identification and regression fitting. It will provide the basis for the application of the mini-MRF damper. (paper)

[en] Fixed in spatial distribution, arrays of planar, electromechanical acoustic transducers cannot adapt their wave energy focusing abilities unless each transducer is externally controlled, creating challenges for the implementation and portability of such beamforming systems. Recently, planar, origami-based structural tessellations are found to facilitate great versatility in system function and properties through kinematic folding. In this research we bridge the physics of acoustics and origami-based design to discover that the simple topological reconfigurations of a Miura-ori-based acoustic array yield many orders of magnitude worth of reversible change in wave energy focusing: a potential for acoustic field morphing easily obtained through deployable, tessellated architectures. Our experimental and theoretical studies directly translate the roles of folding the tessellated array to the adaptations in spectral and spatial wave propagation sensitivities for far field energy transmission. It is shown that kinematic folding rules and flat-foldable tessellated arrays collectively provide novel solutions to the long-standing challenges of conventional, electronically-steered acoustic beamformers. While our examples consider sound radiation from the foldable array in air, linear acoustic reciprocity dictates that the findings may inspire new innovations for acoustic receivers, e.g. adaptive sound absorbers and microphone arrays, as well as concepts that include water-borne waves. (paper)