Junwu Kan

Piezoelectric Bimorph Cantilever for Vibration-Producing-Hydrogen

A device composed of a piezoelectric bimorph cantilever and a water electrolysis device was fabricated to realize piezoelectrochemical hydrogen production. The obvious output of the hydrogen and oxygen through application of a mechanical vibration of ∼0.07 N and ∼46.2 Hz was observed. This method provides a cost-effective, recyclable, environment-friendly and simple way to directly split water for hydrogen fuels by scavenging mechanical waste energy forms such as noise or traffic vibration in the environment.

The Mechanical Property of Magnetorheological Fluid Under Compression, Elongation, and Shearing

The mechanical properties of a MR fluid in compression, elongation, and shearing have been studied in the magnetic field which is generated by a coil carrying different magnitudes of DC electrical current. Test equipment is designed to perform this operation. The compressing tests showed that the MR fluid is quite stiff at small compressive strains being lower than 0.13. The compressive stress and modulus increase quickly when the compressive strain is higher than 0.2. The tensile yield stress of MR fluids represents the effect of the interaction force between the polarized particles and the direction of the applied magnetic field. The shear yield stress represents the effect of the interaction force with the shear direction (perpendicular to the direction of the magnetic field). The relationship between tensile yield stress and shear yield stress verifies the credibility of the calculation model employing a yield angle shaped between particles. A shear yield angle is found to be between about 13.8° and 1...The mechanical properties of a MR fluid in compression, elongation, and shearing have been studied in the magnetic field which is generated by a coil carrying different magnitudes of DC electrical current. Test equipment is designed to perform this operation. The compressing tests showed that the MR fluid is quite stiff at small compressive strains being lower than 0.13. The compressive stress and modulus increase quickly when the compressive strain is higher than 0.2. The tensile yield stress of MR fluids represents the effect of the interaction force between the polarized particles and the direction of the applied magnetic field. The shear yield stress represents the effect of the interaction force with the shear direction (perpendicular to the direction of the magnetic field). The relationship between tensile yield stress and shear yield stress verifies the credibility of the calculation model employing a yield angle shaped between particles. A shear yield angle is found to be between about 13.8° and 16.9°, which agrees with the shear yield angle tested well by other researchers. The tensile yield stress is about four times of shear yield stress.

Development of piezohydraulic actuator driven by piezomembrane pump

A piezohydraulic actuator (piezopump-driven cylinder system) has the advantage over the conventional contact/non-contact piezoelectric motors in terms of achieving large thrust, high velocity, and long traveling distance. In this study, a serial-connection 5-chamber piezomembrane pump (SCCPP) was introduced and used for replacing piezostack pumps so as to decrease cost of piezohydraulic actuators. The border-upon piezomembranes work in anti-phase, a SCCPP is equivalent to several single-chamber pumps running in series. The theoretical study suggests that the performance of a SCCPP-driven actuator depends mainly on the efficiency of check valves, structural parameters of piezomembrane/pump chamber/cylinder, the number of pump chambers, and liquid bulk modulus. A piezomembrane has an optimal thickness ratio (metal to piezoelectric) for the actuator to achieve maximal power. A SCCPP-driven actuator was fabricated and tested under three/four/five chambers running. The testing results show that the thrust, velocity, power, and even optimal frequency of the piezohydraulic actuator all increase linearly with number of working chambers and driving voltage. At 180 V and 280 Hz, the achieved thrust, velocity, power, and step length from the actuator under five piezomembranes running are 75 N, 9.8 mm/s, 184.5 mW, and 35.2 µm, respectively, which are about 2.1/2.7/5.7/2.7 times than those of three piezomembranes running.

Effects of driving mode on the performance of multiple-chamber piezoelectric pumps with multiple actuators

Due to the limited output capability of piezoelectric diaphragm pumps, the driving voltage is frequently increased to obtain the desired output. However, the excessive voltage application may lead to a large deformation in the piezoelectric ceramics, which could cause it to breakdown or become damaged. Therefore, increasing the number of chambers to obtain the desired output is proposed. Using a check-valve quintuple-chamber pump with quintuple piezoelectric actuators, the characteristics of the pump under different driving modes are investigated through experiments. By changing the number and connection mode of working actuators, pump performances in terms of flow rate and backpressure are tested at a voltage of 150 V with a frequency range of 60 Hz −400 Hz. Experiment results indicate that the properties of the multiple-chamber pump change significantly with distinct working chambers even though the number of pumping chambers is the same. Pump performance declines as the distance between the working actuators increases. Moreover, pump performance declines dramatically when the working piezoelectric actuator closest to the outlet is involved. The maximum backpressures of the pump with triple, quadruple, and quintuple actuators are increased by 39%, 83%, and 128%, respectively, compared with the pump with double working actuators; the corresponding maximum flow rates of the pumps are simply increased by 25.9%, 49.2%, and 67.8%, respectively. The proposed research offers practical guidance for the effective utilization of the multiple-chamber pumps under different driving modes.

Performance of a constant-stress piezoelectric generator for battery-less remote control/switch

This paper introduced a novel constant-stress piezoelectr ic cantilever generator (CSPCG) for human-powered battery- less remote controls (switches). The CSPCG consists of a piezoelectric monomorph cantilever and a deflection-limiting device (DLD). The DLD was designed to be a circular arc to shape the bended cantilever and yield constant strain through length. Considering the energy converting ability and reliability, the DLDs radius was figured out as a function of working stre ss and thickness of the piezoelectric plate and substrate plat e. Contrasted with a deflection-free piezoelectric cantile ver generator (DFPCG), the energy performance of the CSPCG was evaluated. Research results show that the two generators share the same optimal thickness ratio for them to achieve the maximal electric energy output. When the same stress and end-deflect ion were provided, the electric-energy generation of the CSPCG is above 4 and 1.5 times that of the DFPCG, respectively. While, the stress and end-deflection of the CSPCG is only 0.49 and 0.7 7 times that of the DFCPG when equal electric energy is generated. This suggests that a CSPCG with a DLD can enhance energy-generating capability and reliability, or decrease end-displacement of piezoelectric cantilever. A CSPCG was fabricated and used to power a low-power remote-control circuit at one-push excitation.

A piezohydraulic vibration isolator used for energy harvesting

A novel piezohydraulic vibration isolator consisting of a hydraulic cylinder and piezodiscs was presented for low-frequency and wide-bandwidth vibration energy harvesting. The analytical model for performance evaluation was established first based on the theory of vibration analysis and simulated to obtain the influence of backpressure and proof mass on equivalent bulk modulus and stiffness of fluid, and optimal frequency and generated voltage of the piezohydraulic vibration isolator. And then, a prototype was fabricated and tested. The research results show that, under other parameters given, the energy generation performance of a piezohydraulic vibration isolator can be tuned with changing backpressure and proof mass. And there are a series of optimal parameter combinations of backpressure and proof mass for a piezohydraulic vibration isolator to achieve the same optimal frequency and almost the same voltage. The minimal optimal tested frequency of 13 Hz and the relative voltage of 81.6 V were obtained at 0.2 MPa and 10 kg. For parameter combinations (0.4 MPa/10 kg, 0.4 MPa/5 kg and 0.8 MPa/5 kg), the optimal frequency and generated voltage are 19 Hz/98 V, 27 Hz/96.8 V and 39 Hz/94.8 V, respectively. Correspondingly, the bandwidths to generate voltage of 40 V are 28/35/30 Hz, respectively.

An investigation of tensile behavior of magnetorheological fluids under different magnetic fields

Stress–strain relationships of magnetorheological fluids under tension tests have been studied over a wide applied magnetic field being generated by a coil carrying different magnitudes of direct current electrical current range. Five tensile behaviors of magnetorheological fluids have been described and explained by structure strengthening effect and decreasing magnetic field strength. The results showed that magnetorheological fluid corresponded to the changes in tensile stress due to the changes in magnetic field. Normalized tensile stress and normalized magnetic field have been proposed to clearly demonstrate the nature of structure strengthening effect during elongation. Under a constant normalized magnetic field, the change of the normalized tensile stress indicated the change of the structure parameter, which showed the existence of structure strengthening effects during elongation. Corresponding to the tensile behavior change, the exponent of tensile yield stress versus magnetic field was also found to vary in different magnetic field ranges.

A piezohydraulic generator for vibration energy harvesting

To improve energy generating capability and reliability/strength, a novel piezohydraulic generator for low frequency vibration was presented. The piezohydraulic generator consisted mainly of a double-rod hydraulic cylinder for conversion of vibration energy to fluid energy and piezodiscs for conversion of the fluidic energy to electric energy. A vibration function and energy-conversion model of the generator was established based on theory of vibration analysis and simulated to obtain the influence of backpressure on energy generation as well as optimal frequency. The analysis results show that both the energy generation and optimal frequency increases with the rising of backpressure under given other parameters. A piezohydraulic harvester was fabricated and tested at different backpressure. Both the optimal frequency and the relative peak voltage/power increase with the rising of backpressure. At 0.2 MPa and 0.8 MPa, the peak-voltage and the relative optimal-frequency are 9 V/11 Hz and 112 V/17.5 Hz respectively. Similarly, the peak-power and the relative optimal-frequency are 0.58 mW/13 Hz and 11.63 mW/17 Hz respectively. The research results indicate that a piezohydraulic generator can be used to harvest energy from a low-frequency and high-level vibration source.

Structure design and experimental study on single-bimorph double-acting check-valve piezoelectric pump

A novel piezoelectric pump called single-bimorph double-acting check-valve piezoelectric pump was proposed in this paper in order to improve the output performance of the single-bimorph single-chamber piezoelectric membrane pump. The constituent parts of the newly designed piezoelectric pump have no difference with the single-bimorph single-chamber check-valve piezoelectric membrane pump except the structural difference of the pump body. There are two serial-connection pump chambers which are formed by the two sides of the piezoelectric bimorph and the pump body of the newly designed piezoelectric pump. The new piezoelectric pump was fabricated, and output performance was experimentally investigated. The maximum flow rate against zero back pressure of the new pump was 318 ml/min and the pumping pressure reached 40.5 kPa at the operating voltage of 90 V. The output power was roughly twice that of the single-bimorph single-chamber check-valve piezoelectric membrane pump. The testing results proved that the new piezoelectric pump could enhance the output performance and the energy conversion efficiency of the piezoelectric bimorph comparing with the single-bimorph single-chamber check-valve piezoelectric membrane pump.

Sensitivity enhancement of piezoelectric force sensors by using multiple piezoelectric effects

The sensitivity enhancement of piezoelectric force sensors is investigated based on multiple piezoelectric effects in this paper. At first, theoretical analysis showed that multiple piezoelectric effects had an influence on the piezoelectric force sensors. Secondly, a practicable method was adopted to perform the experimental validation and quantify the influence of multiple piezoelectric effects. In the method, different capacitors whose capacitances became much larger than that of the piezoelectric quartz sensor were in parallel with the quartz sensor. With the method, the details of the sensitivity enhancement of piezoelectric sensors were obtained. Experimental results showed that the sensor sensitivity increased from 4.00 pC/N to 4.07 pC/N when the capacitance of parallel capacitors was increased from 500 to 1000 and then 5000 times of that of the sensor. The force sensor sensitivity was improved by 1.75%. However, the nonlinearity and repeatability error of the force sensor were markedly increased with increasing the capacitance of the parallel capacitor. The method demonstrated that the piezoelectric force sensor sensitivity could be enhanced to a certain extent in the practical engineering, but it also brought some negative effects. Finally, further analysis indicated that multiple piezoelectric effects influenced the sensitivity by changing the piezoelectric coefficient. The well-known piezoelectric coefficient d11 of the quartz could actually reach 2.35 pC/N.