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Abstract:To lower the operating voltage and improve the output performance of piezoelectric actuators, a multilayer monolithic ultrasonic linear piezoelectric actuator was analyzed with the method of finite element analysis (FEA), and a prototype was fabricated and experimentally researched in this study. Experimental results show that the actuator with a multilayer piezoelectric lead zirconate titanate (PZT) structure (size: 30ˆ7.5ˆ3 mm 3 , mass: 5.49 g) can output a pulling force of 5.0 N maximum and a linear velocity up to 270 mm/s at the voltage of 100 V pp (V pp means the peak-to-peak value of the voltage volts), showing a relatively good velocity controllability at the same time. The temperature rise characteristic of the actuator at various voltages was studied. The results indicate that: the temperature of this actuator rises rapidly but tends to saturate at some value; applying an offsetting voltage or decreasing the amplitude of the voltage would reduce the heat production.

In this study, an oblate-type ultrasonic micro-motor with multilayer piezoelectric ceramic and chamfered driving tips was proposed and experimentally researched. The micro-motor works based on the standing-wave principle and has a higher rotary speed than the traditional standing-wave one in principle, reaching a rotary speed of 2100 r/min in this study at the voltage of 20 V. When the micro-motor rotates, single phase alternating current is required, namely, V=Asinωt, and exchanging the signal wire and ground wire will not change the rotary direction of the motor, which reinforces the safety and the compaction of this motor. The ratio of the maximum displacement value of the speed feeding direction and the preload direction is approximately 4, showing a characteristic of high speed and low ability to load.

This paper presents a new linear piezoelectric actuator, which consists of two pieces of piezoelectric ceramics, a copper substrate and a zirconia driving tip. By changing the input signal, the actuator can be chosen to work in a standing wave mode (two-phase vibration modes coupling) or in a traveling wave mode (four-phase vibration modes coupling). By using the Finite Element Method (FEM), the actuator was designed and optimized, and a prototype was fabricated. For a single actuator at 240Vp-p, the maximum no-load velocity and thrust force were approximately 106 mm/s, 1.2 N in the standing wave mode and 161 mm/s, 1.46 N in the traveling wave mode, respectively. While parallel use of four actuators at the same voltage, the experimental results showed that the velocity and force reached 246 mm/s, 2.2 N in the standing wave mode and 292 mm/s, 4.1 N in the traveling wave mode. More importantly, this study shows that both the load performance and the vibration characteristics of the actuators can be improved greatly by working in the traveling wave mode or parallel distribution of multi-identical piezoelectric actuators.

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In consideration of the thermodynamic parameters of reactants changed along the channel, a new calculation method for the output voltage of PEM (proton exchange membrane) fuel cell was introduced in this paper based on the empirical equations. Then a one dimension steady state model for PEM fuel was established based on this new calculation method. Simulation studies on the distributions of the partial pressure of gases and current density along the channel were implemented with the model. The simulation results showed that, increasing the pressure of inlet gases can increase the partial pressure differences among the sections of the channel, which would deteriorate the uniformity of current density along the channel; A proper increment of the stoichiometric ratio of inlet gases can alleviate the spatial variations of the parameters of reactants, and the uniformity of current density can be improved by such alleviation. In order to validate the effectiveness of the model, the comparison between simulation results and known experimental data was conducted, which indicates that the presented model has proper accuracy.

Condition assessment of cables has gained more attention for the bridge safety. The cable is under tensile load in service. The effect of tensile load for detecting broken wires on parallel wire cable based on guided waves is investigated. The sample cable with broken wires under several levels of tensile load is detected using guided waves based on the magnetostrictive effect. The amplitude of flaw echo increases monotonically with the increasing of tension. The results indicate that the tensile load brings benefit for detecting broken wires in the parallel wire cable.