Tian-Bing Xu

Energy harvesting using a PZT ceramic multilayer stack

In this paper, the interdisciplinary energy harvesting issues on piezoelectric energy harvesting were investigated using a ‘33’ mode (mechanical stress and/or electric field are in parallel to the polarization direction) lead zirconate titanate multilayer piezoelectric stack (PZT-Stack). Key energy harvesting characteristics including the generated electrical energy/power in the PZT-Stack, the mechanical to electrical energy conversion efficiency, the power delivered from the PZT-Stack to a resistive load, the electrical charge/energy transferred from the PZT-Stack to a super-capacitor were systematically addressed. Theoretical models for power generation and delivery to a resistive load were proposed and experimentally affirmed. In a quasi-static regime, 70% generated electrical powers were delivered to matched resistive loads. A 35% mechanical to electrical energy conversion efficiency, which is more than 4 times higher than other reports, for the PZT-Stack had been obtained. The generated electrical power and power density were significantly higher than those from a similar weight and size cantilever-type piezoelectric harvester in both resonance and off-resonance modes. In addition, our study indicated that the capacitance and piezoelectric coefficient of the PZT-Stack were strongly dependent on the dynamic stress. (Some figures may appear in colour only in the online journal)

A single crystal lead magnesium niobate-lead titanate multilayer-stacked cryogenic flextensional actuator

A “33” mode single crystal lead magnesium niobate-lead titanate flextensional actuator with large displacement, high load capability, and broad bandwidth was designed, prototyped, and evaluated at temperatures ranging from room temperature to cryogenic temperatures. Measuring 27.4 × 10 × 13.6 mm (height) overall and weighing 9.2 g, the actuator generates a 96.5 μm displacement in the Z-direction at 170 Vrms. The level of displacement remained constant under compressive loads up to 5 kg force. The actuator maintains 66% of its room temperature displacement at −196 °C. The measured displacements matched well with those modeled using ANSYS finite element analysis.

An electroactive polymer-ceramic hybrid actuation system for enhanced electromechanical performance

A hybrid actuation system (HYBAS) utilizing advantages of a combination of electromechanical responses of an electrostrictive copolymer and an electroactive single crystal has been developed. The system employs the contributions of the actuation elements cooperatively. The theoretical modeling of the performances of the HYBAS is in good agreement with experimental observation. The consistency between the theoretical modeling and the experimental tests makes the design concept an effective route for tailoring and maximizing electrically driven displacement of the hybrid actuation system.

Finite element analysis of the piezoelectric stacked-HYBATS transducer

Finite element modeling (FEM) of a piezoelectric multilayer-stacked hybrid actuation/transduction system (stacked-HYBATS) is investigated in this paper using ANSYS software. This transducer consists of two positive strain components operating in d33 mode and one negative strain component operating in d31 mode to generate large displacements. FEM results are compared with experimental and analytical results to provide insight into the actuation mechanisms, verify the device’s three displacement components, and estimate its blocking force. FEM calculations found the effective piezoelectric coefficient to be exceptional, about 3:11 10 6 pm V 1 at resonance. Stacked-HYBATS was quantitatively compared to commercially available flextensional actuators using finite element analysis. It was found that under the same electric field the yielded displacement of a stacked-HYBATS is about 200% and 15% larger than that of a same-sized d31 and d33 flextensional actuator, respectively. These findings suggest that stacked-HYBATS is promising for precision positioning, vibration control, and acoustic applications. (Some figures may appear in colour only in the online journal)

Piezoelectric vibration energy harvester with two-stage force amplification:

A novel portable energy harvester using 3-3 mode piezoelectric stack with two-stage force amplification is proposed. It can obtain 21 times force amplification with 18% energy transmission ratio and generate electrical energy up to 79 times more than one piezoelectric ceramic of lead zirconate titanate (PZT) stack. Dynamic experiments demonstrate that the harvester with one-and two-stage force amplification can generate the maximum electrical power of 74.9 mW/g2 from one PZT stack at resonance frequency 235 Hz with matching resistance of 268 Ohms and 2642 mW/g2 from three PZT stacks at resonance frequency 37 Hz with match resistance of 1722 Ohm under 100 g proof mass and 0.1 g acceleration. Theoretical electromechanical modeling is established to reveal the working mechanism of force amplification and to predict electricity generation. Comparison of the predicted electricity with experimental results verified effectiveness of electromechanical modeling and optimization design methodology with consideration of tradeoff among force magnification ratio, energy transmission efficiency, and maximum stress. This piezoelectric energy harvester using two-stage force amplification can not only significantly improve power generation but also reduce the resonance frequency Moreover, the resonance frequency can also be adjusted by adjusting the mass load, by which a two-stage energy harvester can be applied to meet requirements of various bandwidths in low-frequency range.

Evaluation of Dielectric-Barrier-Discharge Actuator Substrate Materials

A key, enabling element of a dielectric barrier discharge (DBD) actuator is the dielectric substrate material. While various investigators have studied the performance of different homogeneous materials, most often in the context of related DBD experiments, fundamental studies focused solely on the dielectric materials have received less attention. The purpose of this study was to conduct an experimental assessment of the body-force-generating performance of a wide range of dielectric materials in search of opportunities to improve DBD actuator performance. Materials studied included commonly available plastics and glasses as well as a custom-fabricated polyimide aerogel. Diagnostics included static induced thrust, electrical circuit parameters for 2D surface discharges and 1D volume discharges, and dielectric material properties. Lumped-parameter circuit simulations for the 1D case were conducted showing good correspondence to experimental data provided that stray capacitances are included. The effect of atmospheric humidity on DBD performance was studied showing a large influence on thrust. The main conclusion is that for homogeneous, dielectric materials at forcing voltages less than that required for streamer formation, the material chemical composition appears to have no effect on body force generation when actuator impedance is properly accounted for.

One-dimensional contact mode interdigitated center of pressure sensor

A one-dimensional contact mode interdigitated center of pressure sensor (CMIPS) has been developed. The experimental study demonstrated that the CMIPS has the capability to measure the overall pressure as well as the center of pressure in one dimension simultaneously. A theoretical model for the CMIPS is established here based on the equivalent circuit of the configuration of the CMIPS as well as the material properties of the sensor. The experimental results match well with theoretical modeling predictions. A system mapped with two or more pieces of the CMIPS can be used to obtain information from the pressure distribution in multidimensions.

Optimal design of force magnification frame of a piezoelectric stack energy harvester

With the rapid development of portable electrical devices, the demand for batteries to power these portable devices increases dramatically. However, the development of the battery technology is slow in energy storage capability and cannot meet such requirements. This paper proposed an optimal frame design for a kind of portable piezoelectric stack energy harvesters, with large force magnification ratio and high energy transmission ratio. Two kinds of design approaches have been studied and explored, i.e., flexure compliant mechanism math based and finite element analysis (FEA) based. Prototypes are fabricated and assembled. Experiments with both static test and dynamic test have been conducted to approve the effectiveness of the proposed design. The measured force magnification ratio of 6.13 times and 21.8 times for the first-stage harvester and the dual-stage harvester are close to the design objective of 7.17 times and 24.4 times. The designed single stage harvester can generate 20.7mW/g2 at resonance frequency of 160Hz with optimal resistance of 393Ω under 0.8g base excitation with 100gram top mass, and the dual stage harvester has power generation of 487mW/g2 at resonance frequency of 38.9Hz with optimal resistance of 818Ω under 1.94g base excitation with 100gram top mass. The proposed two-stage PZT energy harvester can be used to develop portable power regenerator to compensate the urgent battery needs in remote area for both civic and military application.

A Piezoelectric PZT Ceramic Mulitlayer Stack for Energy Harvesting Under Dynamic Forces

In this paper, we report the study of a “33” longitudinal mode, piezoelectric PZT ceramic multilayer stack (PZT-Stack) with high effective piezoelectric coefficient for broader bandwidth high-performance piezoelectric energy harvesting transducers (PEHTs). The PZT-Stack is composed of 300 layers of 0.1 mm thick PZT plates, with overall dimensions of 32.4 mm × 7.0 mm × 7.0 mm. Experiments were carried out with dynamic forces in a broad bandwidth ranging from 0.5 Hz to 25 kHz. The measured results show that the effective piezoelectric coefficients (EPC, deff ) of the PZT-stack is about 1 × 105 pC/N at off-resonance frequencies and 1.39 × 106 pC/N at resonance, which is order of magnitude larger than that of traditional PEHTs. The EPC do not change significantly with applied dynamic forces having root mean square (RMS) values ranging from 1 N to 40 N. In resonance mode, 231 mW of electrical power was harvested at 2,479 Hz with a dynamic force of 11.6 Nrms , and 7.6 mW of electrical power was generated at a frequency of 2,114 Hz with 1 Nrms dynamic force. In off-resonance mode, an electrical power of 18.7 mW was obtained at 680 Hz with a 40 Nrms dynamic force. A theoretical model of energy harvesting for the PZT-Stack was established. The modeled results matched well with experimental measurements. This study demonstrated that structures with high EPC enable PEHTs to harvest more electrical energy from mechanical vibrations or motions, suggesting an effective design for high-performance low-profile PEHTs with potential applications in military, aerospace, and portable electronics. In addition, this study provides a route for using piezoelectric multilayer stacks for active or semi-active adaptive control to damp, harvest or transform unwanted vibrations into useful electrical energy.Copyright

Electroactive-polymer-based MEMS for aerospace and medical applications

Electroactive polymers (EAP) demonstrate advantages over some traditional electroactive materials such as electro-ceramics and magneostrictive materials for electromechanical device applications due to their high strain, light weight, flexibility, and low cost. Electroactive polymer-based microelectromechanical systems (EAP-MEMS) are increasingly demanded in many aerospace and medical applications. This paper will briefly review recent progress in the developments and applications of EAP- MEMS. In the past few years, several new configurations of micromachined actuators/transducers have been developed using electroactive polymers. The performance of these micromachined EAP-based devices has been evaluated for both fluid and air conditions. The performance of EAP-MEMS has also been theoretically modeled based on material properties and device configurations. In general, the results obtained from modeling agree with the experimental measurements. Critical process issues, including patterned micro-scale electrodes, molded micro/nano electroactive polymer structures, polymer to electrode adhesion and the development of conductive polymers for electrodes will be discussed. The challenges to develop complete polymer MEMS will also be addressed.