Hairen Wang

A piezoelectric spring-mass system as a low-frequency energy harvester [Correspondence]

We propose a new structure consisting of a piezoelectric spring-mass system as a low-frequency piezoelectric energy harvester. A theoretical model is developed for the system from the theory of piezoelectricity. An analysis is performed to demonstrate the low-frequency nature of the system. Other basic characteristics of the energy harvester, including the output power, voltage, and efficiency, are also calculated and examined.

On the nonlinear behavior of a multilayer circular piezoelectric plate-like transformer operating near resonance

We studied the weakly nonlinear behaviors of a simply-supported multilayer circular piezoelectric plate-like transformer (MCPPT) operating near resonance, where the MCPPT consists of a multilayer circular piezoelectric compound plate with four piezoelectric layers polarized in different directions. Nonlinear effects of large deformations near resonance are considered; it is shown that on one side of the resonant frequency, the output-input relation becomes nonlinear, and the other side, the output voltage becomes multivalued.

On the strain-gradient effects in micro piezoelectric-bimorph circular plate power harvesters

We analyze the first-order gradient effects in micro piezoelectric-bimorph circular plate (PBCP) power harvesters by including the first-order gradient terms in the energy density functions. Considering that the dimension of a PBCP is much smaller in the thickness direction than the in-plane dimensions, the gradient effects can be focused on analysis of the strain-gradient effects in the thickness direction through choosing the strains and the electric displacements as the independent constitutive variables. The paper has shown theoretically that the first-order gradient effects have induced shift in the natural frequency of a PBCP structure and resulted in a small change in the harvester performance.

Analytical analysis of a beam flexural-mode piezoelectric actuator for deformable mirrors

Abstract. A beam flexural-mode piezoelectric bimorph actuator is analyzed based on linear piezoelectricity, and the performance of the actuator is studied. The beam bimorph piezoelectric actuator (BBPA), which is a sandwich compound consisting of a lower and an upper piezoelectric ceramic surface layer and a middle layer made of metal, is driven to flexural deformation. The statistical analytical solution and dynamical solutions from the three-dimensional equations of linear piezoelectricity are derived, and the dependence of the performance upon the physical parameters of the BBPA is evaluated. Numerical results illustrate the strengthened performance achieved by adjusting the geometrical and material parameters of the BBPA.

Nonlinear analysis of a 5-layer beam-like piezoelectric transformer near resonance

The paper examines the weakly nonlinear behavior of a 5-layer beam-like piezoelectric transformer operating near resonance, where the main structure of the device consists of properly poled and electroded flexible piezoceramic four-layers separated by a central metallic layer. Nonlinear effects of the large deflection to induce the incidental in-plane extension near resonance are considered, which is shown that on one side of the resonant frequency the output-input relation becomes nonlinear, and the other side output voltage experiences jumps.

Adjusting the resonant frequency of a segmented energy harvester through circuit connection patterns

We propose a segmented piezoelectric energy harvester in the flexural mode for scavenging ambient vibration energy. 4 circuit connection patterns between segment piezoelectric bimorphs are presented. The resonant frequency of a segmented piezoelectric harvester is readily adjusted through changing either its geometrical configuration or circuit connection pattern, which can keep the harvester operating at the optimal state in environment with different ambient vibrations. The governing equations of a segmented piezoelectric harvester with alternate bimorphs are derived from the transfer-matrix technique. The numerical results show that the adaptability of a harvester to the operating environment can be improved greatly by designing the harvesting structure with adjustable resonant frequency.

Numerical analysis on an annular bimorph piezoelectric power harvester with the out-of-plane vibration mode

This paper proposes a piezoelectric annular bimorph power harvester (PABPH) aiming at scavenging mechanical vibration energy exists in the ambient environment. Abundant energy of the ambient vibration mainly contains in low frequency. In order to decrease the resonate frequency and miniaturize the device, finite element model is present for the harmonic and modal analysis of the PABPH. Numerical results show that maximum of the output power density of the PABPH does not always appear on its first resonance frequency. The resonance frequency depends on the structure parameters of the PABPH, such as the length and the thickness. After being optimized on length of annular plate and thickness of metal layer, the PABPH has an output power density of 36 µW / cm3 when driven by ambient vibration with amplitude of 1mN and frequency of 50 Hz.

Experimental research on nonlinear coupling between two sides of rectification in piezoelectric energy harvester

This paper proposes a piezoelectric energy harvester experiment model, which composed of piezoelectric harvesting element, energy storage element, and a full bridge to connect them as an integrated system. A synchronized switch harvesting inductor (SSHI) is introduced in parallel with the harvesting structure to reverse voltage through the charge transfer between the output electrodes at the transition moments from closed- to open- circuit, i.e. the time when the harvesting structure deforms to the extreme position. The harvesting structure is driven to vibrate by vibration exciter which is acted by a voltage signal with a certain frequency. The method of capturing zero velocity is used to catch the moment when the harvesting structure deforms to the extreme position. SSHI closes synchronously, and delay a half period of the oscillator, composed by the inductor and effective capacitor of piezoelectric harvesting structure, then opens. This process is controlled by the technique of single chip microcomputer. Experimental results show SSHI processes have been achieved. An optimal rectified voltage can maximize the output power density of the piezoelectric energy harvester.