Li Sui

Performance of pre-deformed flexible piezoelectric cantilever in energy harvesting

This paper proposes a novel structure for pre-rolled flexible piezoelectric cantilevers that use wind energy to power a submunition electrical device. Owing to the particular installation position and working environment, the submunition piezoelectric cantilever should be rolled when not working, but this pre-rolled state can alter the energy harvesting performance. Herein, a working principle and installation method for piezoelectric cantilevers used in submunitions are introduced. To study the influence of the pre-rolled state, pre-rolled piezoelectric cantilevers of different sizes were fabricated and their performances were studied using finite element analysis simulations and experiments. The simulation results show that the resonance frequency and stiffness of the pre-rolled structure is higher than that of a flat structure. Results show that, (1) for both the pre-rolled and flat cantilever, the peak voltage will increase with the wind speed. (2) The pre-rolled cantilever has a higher critical wind speed than the flat cantilever. (3) For identical wind speeds and cantilever sizes, the peak voltage of the flat cantilever (45 V) is less than that of the pre-rolled cantilever (56 V). (4) Using a full-bridge rectifier, the output of the pre-rolled cantilever can sufficiently supply a 10 μF capacitor, whose output voltage may be up to 23 V after 10 s. These results demonstrate that the pre-rolled piezoelectric cantilever and its installation position used in this work are more suitable for submunition, and its output sufficiently meets submunition requirements.

Buckling analysis of planar compression micro-springs

Large compression deformation causes micro-springs buckling and loss of load capacity. We analyzed the impact of structural parameters and boundary conditions for planar micro-springs, and obtained the change rules for the two factors that affect buckling. A formula for critical buckling deformation of micro-springs under compressive load was derived based on elastic thin plate theory. Results from this formula were compared with finite element analysis results but these did not always correlate. Therefore, finite element analysis is necessary for micro-spring buckling analysis. We studied the variation of micro-spring critical buckling deformation caused by four structural parameters using ANSYS software under two constraint conditions. The simulation results show that when an x-direction constraint is added, the critical buckling deformation increases by 32.3-297.9%. The critical buckling deformation decreases with increase in micro-spring arc radius or section width and increases with increase in micro-spring thickness or straight beam width. We conducted experiments to confirm the simulation results, and the experimental and simulation trends were found to agree. Buckling analysis of the micro-spring establishes a theoretical foundation for optimizing micro-spring structural parameters and constraint conditions to maximize the critical buckling load.

Micro-Spring’s Variable Stiffness Design and Characteristics Analysis

The variable stiffness micro-springs’ load and deformation have nonlinear relationship, thus they can be used in special occasions. MEMS processing technology can manufacture any complex structures in a plane, using this feature, a variable stiffness design idea for the planar micro-spring is proposed. That is, using one type of structure named contact pairs to achieve stiffness change during the micro-spring’s stretching process. Using contact pairs, two types of variable stiffness springs are designed: stiffness increase spring and stiffness convexity spring. Because of the influence of processing precision, the contact pairs’ sizes of the first type of variable stiffness spring are different each other, the machining error makes the test results and simulation results various. In order to avoid the above problem of above spring, this paper designs another two variable stiffness micro-springs, test results indicate that the improved variable stiffness springs can realize the variable stiffness’ tendency.

Research Survey of Electroformed Nickel Material Properties Used in MEMS

As one of the significant structural materials used in safe and arming system of MEMS fuze, the research on micro-electroforming process technologies and micro-electroforming nickel’s properties have been a popular field for MEMS area. This paper surveys present domestic and overseas research status of mechanical characterization of electroformed nickel, summarizes and analyzes that changes of the microstructure led by parameters of micro-electroforming process and the external environment make great effects.

The application of multilayer elastic beam in MEMS safe and arming system

In this paper, a new approach for a multilayer elastic beam to provide a driving force and driving distance for a MEMS safe and arming system is presented. In particular this is applied where a monolayer elastic beam cannot provide adequate driving force and driving distance at the same time in limited space. Compared with thicker elastic beams, the bilayer elastic beam can provide twice the driving force of a monolayer beam to guarantee the MEMS safe and arming systems work reliably without decreasing the driving distance. In this paper, the theoretical analysis, numerical simulation and experimental verification of the multilayer elastic beam is presented. The numerical simulation and experimental results show that the bilayer elastic provides 1.8–2 times the driving force of a monolayer, and a method that improves driving force without reducing the driving distance.

The Electricity Performance of Flexible Piezoelectric Generator

A FPEG (flexible piezoelectric generator) composed of PVDF (polyvinylidene fluoride) piezoelectric film, conducting resin and titanium alloy substrate, which occupies less room and produces electrical energy while the axial wind flows through the oscillator surface. When the axial wind flows through the generator surface, generator begins to vibrate and produce electrical energy, as the wind speed reaches a critical value, generator yields resonance phenomenon. In this paper, more work was placed on how the substrate structure parameters such as length, width and thickness affected the power generation capacity in resonance mode.

Low Stress MEMS Delay Mechanism

For the existing symmetry Z-tooth MEMS delay mechanisms can not play sports in place under the influence of centrifugal force, this paper presents an asymmetric Z-tooth delay mechanism which can works reliably by weak environmental forces. Working principle and the stress condition of the mechanism are analyzed. Based on the dynamic model, this paper makes a computational analysis and simulation about the kinetic characteristics of the asymmetric Z-tooth delay mechanism, and the results show that the improved mechanism can works reliably and meets the requirements.