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This paper presents the modeling and experimental parametric study of a nonlinear multi-frequency broad bandwidth piezoelectric vibration-based energy harvester. The proposed harvester consists of a tri-leg compliant orthoplanar spring (COPS) and multiple masses with piezoelectric plates attached at three different locations. The vibration modes, resonant frequencies, and strain distributions are studied using the finite element analysis. The prototype is manufactured and experimentally investigated to study the effect of single as well as multiple light-weight masses on the bandwidth. The dynamic behavior of the harvester with a mass at the center is modeled numerically and characterized experimentally. The simulation and experimental results are in good agreement. A wide bandwidth with three close nonlinear vibration modes is observed during the experiments when four masses are added to the proposed harvester. The current generator with four masses shows a significant performance improvement with multiple nonlinear peaks under both forward and reverse frequency sweeps. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting is envisioned as an ideal complement to batteries for long-life operation of wireless or remote electronic devices. Most piezoelectric energy harvesters (PEHs) utilize piezoelectric plates or discs as the energy transducing elements, and they cannot generate enough power for most potential applications. In this study, we explore a new way of using arc-shaped piezoelectric patches as the core transducing elements in energy harvesters to improve their performance. An analytical model is developed via the Castigliano’s theorem to elucidate the low stiffness characteristic of the arc-shaped structure. A finite element analysis is conducted, and the results indicate that high and evenly-distributed stress can be easily induced in the arc-shaped PEHs. Prototypes are fabricated with arc-shaped piezoelectric elements and flat piezoelectric plates, respectively, and tested under the same conditions. The experimental data demonstrate that the arc-shaped PEHs are capable of generating 2.55–4.25 times as much power as the equivalent flat-plate PEHs. This study lays the foundation to enhance energy harvester performance by utilizing arc-shaped piezoelectric structures. [ABSTRACT FROM AUTHOR]

• Multiple nonlinear energy harvesters are developed based on compliant orthoplanar springs and piezoelectric materials. • Experiments with both harmonic and random excitations are performed. The proposed COPS harvesters could show an extended operational bandwidth in both conditions. • The study quantitatively demonstrates the effectiveness of interaction of multiple nonlinear vibration modes on harvester performance enhancement, and which effect can be tuned by the addition of multiple masses and spring legs. • The quad-leg design shows a broad bandwidth of 35 Hz while maintaining a voltage response of 4 V. This paper compares the performance of three nonlinear compliant orthoplanar springs, namely, bi-leg, quad-leg and pent-leg designs to study the vibration mode interaction effect for widening the operational bandwidth of piezoelectric vibration energy harvester. All the designs have three or more vibration modes below 150 Hz with the addition of multiple masses. Finite element analysis results of spring designs and vibration mode shapes are presented and compared with experiments. The prototypes were manufactured and experimentally tested to analyze their dynamic voltage-frequency responses and operational bandwidths under sinusoidal and band-limited excitations. The experimental results demonstrate that the operational bandwidth is significantly broadened by the geometric nonlinearity of the structure. The addition of multiple masses brings the vibration modes of the system closer, and thus further helps to extend the operational bandwidth. In addition, we introduce multiple piezoelectric plates into harvesters to enable energy harvesting in all vibration modes. The quad-leg design shows the largest frequency bandwidth of 35 Hz, maintaining a peak-to-peak voltage of 4 V under the forward frequency-sweep excitations. Under the reverse frequency-sweep excitations, the voltage response and the operational bandwidth are comparable to those of the forward-sweep ones as a result of continuous overlapping of linear and nonlinear voltage peaks. Random excitation experiments demonstrate the effectiveness of the proposed mutli-leg structure in harvesting energy from wideband environmental vibrations. [ABSTRACT FROM AUTHOR]

Highlights: • Improved harvester power output via abrupt magnetic-flux-density changes. • Fabricated magnet arrays of alternating north and south poles to abrupt flux changes. • Constructed alternative and Halbach arrays with triangular and cubic magnets. • Achieved a max RMS power output of 35.5 mW under an excitation of 9.8 m/s2. Abstract Electromagnetic energy harvesters have been studied intensively in the past decade as non-stop power solutions for low-power wireless electronic devices. We here exploit a new way, i.e., forming an abrupt change of magnetic flux density, to improve harvester performance. A new transducer is proposed, which is primarily composed of a set of magnet array, a pair of springs and a coil array. Four cases are investigated: cubic magnets in Halbach and alternative configurations; triangle magnets in Halbach and alternative configurations. We examined the magnetic flux density distribution via the finite element method (FEM) and ensured the nonexistence of phase difference in two contiguous coils. We fabricated a prototype and conducted comprehensive tests, of frequency sweep with and without external resistances, of matching impedance and of obtaining maximum RMS power output. The FEM analysis indicates that the harvester in the cubic alternative case has the largest changing rate of the magnetic flux density (MFD) in terms of the magnitude and the distance range of the change. Experiments verify the FEM simulation and the prototype with the cubic alternative magnet array shows the highest voltage response of 20 V and a maximum RMS power output of 35.5 mW under a harmonic excitation of 9.8 m/s2, which is much higher than those in the other cases. In term of the volume and mass power density, the alternative arrangement of cubic magnets displays the most desirable outputs at 0.4955 mW/cm3 and 0.28 mW/g, respectively, which are three and two times as high as those of the second best case - the triangle Halbach case. This detailed study reveals the considerable benefits brought by the magnet arrays of alternating polarity and configuration, and paves a new way to improve the performance of electromagnetic energy harvesters. [ABSTRACT FROM AUTHOR]

• T-phage-inspired multilegged design for microrobot. • A rotationally asymmetric structure. • Multiple working modes: forward motion, backward motion, steering, climbing, and swimming. • The maximum velocity of 120 mm/s under a driving voltage of 50 V p-p and the maximum carrying weight of 10.6 gs, 6 times more than the weight of the microrobot. • Miniaturization capability and ability to work in various environments, i.e., a narrow tube and water. T-phages use contractile tails to recognize host bacterial and move on the surface of bacterial. This virus demonstrates remarkable locomotive capabilities in recognition and infection progress. The field of microrobotics focuses on achieving these functions in mobile robotic systems of centimeter size. However, owing to the structure size and weight, it has been a challenge to satisfy high robustness, fast motion, adequate carrying capacity, low driving voltage, and versatile environmental adaptability in one robot. In addition, functional microrobots require multimodal locomotive strategies that reconcile the constraints imposed by different applications. Inspired by the unique structure of T-phage in the micro-world, we develop a T-phage Mimic MicroRobot (TMMR), which is composed of a triangular prism core with piezoelectric elements and legs attached on bases, mimicking the core and the tail fibers of the T-phage, respectively. The triangular prism structure avoids rollover while moving, indicating the robustness of the design. TMMR of 2.5 × 2.5 × 2.6 mm3 weighs 1.74 gs and can be easily further miniaturized. It is capable of moving forward, backward, and steering at a low voltage of 25 V. Working mechanisms for each type of motion are analyzed using the finite element method. Results show that TMMR reaches 120 mm/s, 4.8 body lengths per second (BL/s), and carry an object weighing 10.6 gs, 6 times more than its weight. By sealing the body and adding passive flaps, TMMR achieves a "swimming" motion with a velocity of 16 mm/s. TMMR shows potential for versatile applications in a narrow and constrained environment. [Display omitted] [ABSTRACT FROM AUTHOR]

• Distributed-parameter model for a doubly-clamped energy harvester affected by the misalignment-induced torsions in vibration environments. • Experimental validation for the developed model and the effects of the bending-torsional coupling vibration on the harvester. • Characterizations of the bending-torsional coupling vibration for the doubly-clamped beam structures. • Investigations on the effects of the key parameters on the torsion-induced jump-down phenomenon. This article presents a theoretical and experimental study on the unique bending-torsional coupling vibration of a doubly-clamped nonlinear piezoelectric energy harvester due to the misalignment of the centroid and the torsional axis in vibration environments. Based on the Euler-Bernoulli beam theory, the extended Hamilton's principle, and the Galerkin discretization, a distributed-parameter model considering the misalignment is developed, and the corresponding governing equations are formulated. The developed model is validated against experimental data and Finite Element Analysis, where good agreements are achieved. Effects of the key parameters on the system's responses, and the characteristics and the causes of the bending-torsional coupling vibration are studied numerically based on the developed model. The results show that the torsion-induced chaotic motion can activate the jump-down phenomenon, largely reducing the electrical output of the harvester. Additionally, the occurrence of the torsion-induced jump-down phenomenon is sensitive to the system's initial state in some cases and can be reduced or even avoided by effectively tuning parameters that have slight effects on the bending resonance, such as the preloaded axial force and the distance between the torsional axis and the centroid. [ABSTRACT FROM AUTHOR]

[Display omitted] • Propose an auxetic nonlinear piezoelectric energy harvester. • Utilize a pure mechanical structure to enhance both efficiency and bandwidth. • Perform finite element analysis to analyse the performance of the harvester. • Experimentally validate the proposed design and model and conduct parametric studies. In this paper, we design and experimentally validate an auxetic nonlinear piezoelectric energy harvester. This harvester adopts a clamp-clamp beam with auxetic structures, which can improve the efficiency and bandwidth of the energy harvesting based on a pure mechanical structure without outer magnets or stoppers. Finite element analysis is performed to analyse the effects of the auxetic structures on the efficiency and nonlinearity of the energy harvester. The lumped parameter model is utilized to predict the performance of the energy harvester, which well matches the experimental results. In the experimental validation, at 0.1 g base acceleration, the power output of the two types of auxetic energy harvesters is 173% and 94% higher than the conventional nonlinear energy harvester. Besides, the bandwidths of the two types of auxetic energy harvesters are broadened by 1556% and 2142% compared with the linear systems. [ABSTRACT FROM AUTHOR]

• Segmented arc-shaped piezoelectric energy harvester is proposed. • A new distributed-parameter electromechanical coupling model is developed. • The analytical solutions are validated with FEM and experiments. • Energy harvester characteristics with optimal parameters to generate maximum output voltage of 50 V are fully investigated. Advances in energy harvesting techniques, along with low-power electronic devices open up the possibility of developing self-powered engineering systems. Most existing energy harvesters are constructed with beams such as cantilevers, fully-clamped beams and buckled beams. Here we present an attempt to add a new design dimension to the piezoelectric energy harvesters (PEHs) by exploiting a curved-beam structure. This design will be shown to dramatically improve the contemporary harvester performance. To establish an analytical base for curved PEHs, we take a variable-curvature unimorph as the general modelling object and derive its governing equations based on the Timoshenko beam theory. Using the mode expansion method with the consideration of boundary conditions and continuous conditions, we present analytical solutions of the electrical and mechanical response of the PEH. The model developed is verified via the finite element method and it can accurately estimate the modal response of the curved PEH. Prototypes are fabricated and tested to validate the analytical model and solutions. Furthermore, we comprehensively analyzed the key parameter effects including the length of the straight beam, thickness ratio and Young's modulus on the performance of the PEH. The proposed analytical model provides an analytical guidance for composite arc-shaped PEHs with variable curvature and it also helps in the design and optimization of new PEHs. [ABSTRACT FROM AUTHOR]