Cheng Liang Pan

Power density of piezoelectric transformers improved using a contact heat transfer structure

Based on contact heat transfer, a novel method to increase power density of piezoelectric transformers is proposed. A heat transfer structure is realized by directly attaching a dissipater to the piezoelectric transformer plate. By maintaining the vibration mode of the transformer and limiting additional energy losses from the contact interface, an appropriate design can improve power density of the transformer on a large scale, resulting from effective suppression of its working temperature rise. A prototype device was fabricated from a rectangular piezoelectric transformer, a copper heat transfer sheet, a thermal grease insulation pad, and an aluminum heat radiator. The experimental results show the transformer maintains a maximum power density of 135 W/cm3 and an efficiency of 90.8% with a temperature rise of less than 10°C after more than 36 h, without notable changes in performance.

Coupled torsional and longitudinal vibrations of piezoelectric fiber actuator with helical electrodes

The vibration characteristics of a piezoelectric fiber actuator with helical electrodes are studied theoretically and experimentally. Its working principle indicates that the torsional, longitudinal, and tangential deformations of the fiber are coupled. A simplified dynamic model is deduced to investigate the properties of the coupled vibrations and their corresponding equivalent circuits are also provided. Resonant frequencies and mechanical coupling coefficients in free-free boundary condition are calculated. The trends of resonant frequencies as functions of the electrode helical angle and fiber length are discussed and validated in experiments.

Analysis of the actuating effects of triple-layer piezoelectric cantilevers considering electromechanical coupling correction

A dynamic analytical model is developed to predict the performance of a triple-layer piezoelectric cantilever as actuators in relation to materials with large piezoelectric and electromechanical coupling (EMC) coefficients under axial stress and plane strain conditions. The dynamic electromechanical behavior of a symmetrical triple-layer piezoelectric cantilever (STLPC) actuator is investigated. The analytical model of STLPC based on electromechanical coupling correction coefficient (EMCC) is established in one-dimensional (1D) form and applied to 1D and 2D deformations. Furthermore, the theoretical analysis of the EMCC model is critically evaluated and compared with the simulations using a finite element method (FEM). Results show that the EMCC model can be accurately applied to analyze the actuation performance of STLPC. Analyzed results show that the proposed model is accurately applied to large and small piezoelectric coupling conditions. The piezoelectric cantilever with large piezoelectric and EMC coefficients can be accurately analyzed by the proposed model accounted for small EMC condition in a traditional model. Design optimization based on actuators is also discussed. Optimal thickness ratios between elastic and piezoelectric layers are effectively calculated and obtained.

Theoretical analysis of dynamic property for piezoelectric cantilever triple-layer benders with large piezoelectric and electromechanical coupling coefficients

Ferroelectric single crystals, such as PZN-PT, provide novel prospects in piezoelectric bending devices such as actuators, sensors or energy harvesters because of their extraordinarily large piezoelectric coefficients. However, large errors may occur in some analyses on electromechanical behaviors using the conventional models. We find the bending rigidity of piezoelectric composited bender is affected not only by thickness, width and the modulus of elasticity of the different layers but also electromechanical coupling coefficients (EMCCs) of the piezoelectric material and the larger EMCCs mean more marked effect. This paper focuses on the derivation of the applied input excitation and output response characteristics in the circular frequency domain for piezoelectric cantilever triple-layer benders (PCTBs), taking into account the secondary piezoelectric effect. Analytic dynamic descriptions of such actuators and transducers are obtained. Based on the presented models dynamic features of PCTB composed of PZN-8%PT are calculated, and numerical results coincide with simulations using the finite element method (FEM).

Piezoelectric tube with helical electrodes: Numerical analysis of actuator and energy harvesting devices

This article presents a finite element analysis of a polarized piezoelectric tube driven by helical electrodes. It is thanks to a helical coordinate meshing and local coordinate system association with each element that the problem of piezoelectric coupling has been studied. The numerical results agree well with the experimental data without the need of compensation factors as in previous works. The developed model was used to determine the electromechanical coupling coefficients of the tubes in axial and torsional modes. The electromechanical coupling coefficient depends on the helical angle of the electrode. In the axial mode, electromechanical coupling coefficient goes through a maximum value of 25% when the helical angle of the electrode is close to 30°, while in the torsional mode, the maximum value of electromechanical coupling coefficient was reached at a helical angle near 60°. The analysis investigates the tube size effects and shows the potential uses of piezoelectric tubes as an actuator or energy harvesting device. The presented model could be used to analyze the electric fields in the tube during the polarization process or to analyze the mechanical stress (without any limitation due to Saint-Venant’s principle) imposed by the simplified analytical approaches available in the literature. The developed approach can also be used for theoretical analysis of the helical/spiral piezoelectric element.

Dual-branch reed for resonant cavity wind energy harvester with enhanced performances:

A structure of dual-branch piezoelectric unimorph reed with the resonant cavity of a harmonica to harvest wind energy for the wireless sensor networks was introduced in this paper. After the experiments and simulation analysis, a new mathematical model was established for further research on this structure. The vibration of the reed in the resonant cavity was dealt with as the damping forced vibration of a triangular pulse excitation. This model well explained why the dual-branch reed can vibrate much stronger than the no-branch reed. The experiment proved that the proposed structure and model are feasible and efficacious, the dual-branch reed not only increases the vibration amplitude of the piezoelectric reed but also exhibits a wide wind speed range. A prototype wind energy harvester with a wind inlet dimension of 25 mm × 25 mm can generate an maximum power of 6.7 mW and have an efficiency of 3.5%, with wind speed from 3.2 m/s to 16 m/s.

Piezoelectric Power Transceiver with Ultra-High Isolation

An electric power transceiver with ultra-high isolated is presented in this paper. Two pieces of piezoelectric elements serving as energy transmitter and energy receiver are attached to two ends of a slender glass beam, respectively. The slender glass beam with dimensions of 500 mm(L)×20 mm(W)×2 mm(T) is used as the media of vibration to realize wireless power transmitting. A distance of 396 mm between the two piezoelectric elements ensures an ultra-high isolation between the input and output circuit. The system is designed and analyzed by finite element method. Experiment tests are also conducted to investigate the performance of the transceiver. With a matched load resistance of 500 Ω, the transceiver can work continuously and stably with an output power of 3 W (no heat sinking) and an efficiency of 60%.

A high-sensitive static vector magnetometer based on two vibrating coils

A static vector magnetometer based on two-dimensional (2D) vibrating coils actuated by a piezoelectric cantilever is presented. Two individual sensing coils are orthogonally fastened at the tip of cantilever and piezoelectric sheets are used to excite the cantilever bending. Due to off-axis coupler on the tip, the cantilever generates bending and twisting vibrations simultaneously on their corresponding resonant frequencies, realizing the 2D rotating vibrations of the coils. According to Faraday-Lenz Law, output voltages are induced from the coils. They are amplified by a pre-amplifier circuit, decoupled by a phase-sensitive detector, and finally used to calculate the vector of magnetic field at the coil location. The coil head of a prototype magnetometer possesses a dc sensitivity of around 10 μV/Gs with a good linearity in the measuring range from 0 to 16 μT. The corresponding noise level is about 13.1 nT in the bandwidth from 0.01 Hz to 1 Hz.