Zhihua Feng

Right-angle piezoelectric cantilever with improved energy harvesting efficiency

This paper reports a piezoelectric device based on a cantilever with an extended auxiliary part that forms a right angle with the basic part. Theoretical analyses and experiments support that, by using such a device, uniform strain distribution in piezoelectric element surfaces can be obtained, and thus the piezoelectric materials can be used more efficiently. A piezoelectric element on a right-angle cantilever can generate a useful power twice that of a traditional cantilever under the same strain limitation.

Maximum mechanical energy harvesting strategy for a piezoelement

The electromechanical conversion capacity of a piezoelectric power generator is investigated by considering a quasi-static work cycle. How the maximum energy can be harvested from a piezoelectric element limited by its maximum parameters such as the maximum strain, maximum field, maximum surface charge density and maximum stress is detailed in this paper. The work cycle in which the electric field and the stress are controlled in a way designed to get the most energy is illustrated. A contrast has been made between synchronized switching harvesting with an inductor (SSHI) and the methods introduced here, and it is pointed out theoretically that the proposed method yields more power than SSHI.

Piezoelectric Wind-Energy-Harvesting Device with Reed and Resonant Cavity

A wind-energy-harvesting device utilizing the principle of a harmonica was created. A reed in a resonant cavity vibrated efficiently with the blowing wind, and a piezoelectric element stuck on the reed generated electricity. The dimensions of the wind inlet were approximately 30×20 mm2. The device was investigated with a wind speed ranging from 2.8 to 10 m/s. An output power of 0.5–4.5 mW was obtained with a matching load of 0.46 MΩ. The energy conversion efficiency of the device could reach up to 2.4%.

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.

Note: Creep character of piezoelectric actuator under switched capacitor charge pump control

A major deficiency in piezoelectric actuator performance is caused by hysteresis and creep effects. Switched capacitor charge pump control was previously proved to be an effective way to reduce hysteresis. In this work, creep character of a piezoelectric stack under charge pump control is investigated and modeled. Experiments show that the creep can be reduced by about 77% compared with the one under voltage control. The creep factor denoting the degree of creep shows hysteresis loops similar to displacement outputs under voltage control.

A compact and high flow-rate piezoelectric micropump with a folded vibrator

This paper presents the design, fabrication, dynamic analysis, and experimental results of an efficient resonantly-driven piezoelectric micropump. The micropump consists of a folded vibrator, two polydimethylsiloxane (PDMS) check valves and compressible spaces. A newly developed folded vibrator with piezoelectric sheets serves as the resonantly-driven actuator. The vibrator provides uniform strain distribution in piezoelectric sheets surfaces to improve their utilizing efficiency. The PDMS check valves used in this design increase pump’s working stability and largely reduce the leakage rate. In addition, the performance of the micropump is significantly improved by two compressible spaces near the check valves. Experimental results on a prototype with dimensions of 20 mm×20 mm×28 mm demonstrate that the maximum flow rate of 118 ml min �1 and maximum back pressure of 22.5 kPa are obtained when the micropump is driven by a sinusoidal voltage of 120 Vpp at 361 Hz. A stable minimum flow rate of 160 μl min �1 can be obtained with driving voltage of 4 Vpp. The maximum power consumption of the micropump is approximately 62 mW for 118 ml min �1 at zero backpressure.

An impact rotary motor based on a fiber torsional piezoelectric actuator

A prototype small impact rotary motor has been fabricated based on a newly developed torsional actuator which is 15.0 mm long and 1.0 mm in diameter. The motor can rotate when it is powered with a saw-shaped voltage. The experimental results show that its angular speed is proportional to both the driving voltages amplitude and the frequency under 1 kHz. The large nonlinearity occurs at higher driving frequency due to the resonance of the partial mechanical structure of the motor. The motor can rotate at a speed of 90 rpm with a saw-shaped driving voltage of 600 V(p.-p.) at 8 kHz, and produce a stall torque of 80 microN m with 1000 V(p.-p.) at 3 kHz.

Noncontact Thickness Measurement of Metal Films Using Eddy-Current Sensors Immune to Distance Variation

A simple method for measuring the thickness of metal films based on eddy-current sensors (ECSs) immune to distance variation is proposed. The slope of the lift-off curve (LOC) in the RL impedance plane is a good feature for characterizing target thickness independent of lift-off distance variation. A simple equivalent model was built to deal with the ECS problem, and the essential relationship between the slope of LOC (SLOC) and target properties was obtained. Full finite element analysis was conducted to analyze the relationship between SLOC feature and target thickness, and the results matched the modeling results very well. A sensor coil probe was then manufactured and used to measure the thickness of copper films with high performance, and the capability of this technique for online noncontact thickness measurement was verified. The basic characteristics and performances of this thickness measurement technique were tested and discussed. The SLOC feature for thickness measurement had significant advantages, such as simplicity, reliability, immunity to the lift-off effect (most important), high speed, simple signal processing, and negligible design limitation of the sensor probe. The results of this paper revealed that online thickness measurement systems could be developed for various advanced industrial applications.

Harvesting vibration energy using two modal vibrations of a folded piezoelectric device

This letter reports a piezoelectric vibration energy harvester that uses the local lateral resonant modes of a folded structure to widen the operation frequency band. In addition, energy conversion efficiency is improved. A prototype energy harvester was fabricated and tested. The output power achieved two power peaks: 0.43 mW at 97 Hz and 6.64 mW at 120.9 Hz. The output power remained above 20 μW within the operation frequency band that ranged from 88 Hz to 177 Hz when the energy harvester was driven with a vibration of 0.7 g peak acceleration. The output power remained higher than half of one of the maximum power peaks (0.43 mW) between 95 Hz and 101 Hz. Meanwhile, it remained higher than half of the other maximum power peak (6.64 mW) between 120.5 Hz and 123.8 Hz.

Small torsional piezoelectric fiber actuators with helical electrodes

Small piezoelectric fibers wound with helical electrodes on their outer surface will produce torsional displacement. A piece of piezoelectric tube with an outer diameter of 1mm, a wall thickness of 0.1mm, and an effective axial length of 40mm was used as a prototype actuator’s body, while two pieces of copper wires of 40μm diameter were used as the electrodes. After poled with 2kV∕mm electric field strength, the prototype actuator produces 1.7° torsional angle when it was driven from −500to500V. A resonant frequency as high as 10kHz was observed on this actuator.