Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezo...Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezoelectric energy harvester （PEH） is usually designed as a linear resonator, and suffers from a narrow operating bandwidth. To achieve broadband energy harvesting, in this paper we introduce a concept and describe the realization of a novel nonlinear PEH. The proposed PEH consists of a primary piezoelectric cantilever beam coupled to an auxiliary piezoelectric cantilever beam through two movable magnets. For predicting the nonlinear response from the proposed PEH, lumped parameter models are established for the two beams. Both simulation and experiment reveal that for the primary beam, the introduction of magnetic coupling can expand the operating bandwidth as well as improve the output voltage. For the auxiliary beam, the magnitude of the output voltage is slightly reduced, but additional output is observed at off-resonance frequencies. Therefore, broadband energy harvesting can be obtained from both the primary beam and the auxiliary beam.展开更多
The strategy of incorporating polymers into MXene-based functional materials has been widely used to improve their mechanical properties,however with inevitable sacrifice of their electrical conductivity and electroma...The strategy of incorporating polymers into MXene-based functional materials has been widely used to improve their mechanical properties,however with inevitable sacrifice of their electrical conductivity and electromagnetic interference(EMI)shielding performance.This study demonstrates a facile yet efficient layering structure design to prepare the highly robust and conductive double-layer Janus films comprised of independent aramid nanofiber(ANF)and Ti3C2Tx MXene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)layers.The ANF layer serves to provide good mechanical stability,whilst the MXene/PEDOT:PSS layer ensures excellent electrical conductivity.Doping PEDOT:PSS into the MXene layer enhances the interfacial bonding strength between the MXene and ANF layers and improves the hydrophobicity and water/oxidation resistance of MXene layer.The resultant ANF/MXene-PEDOT:PSS Janus film with a conductive layer thickness of 4.4μm was shown to display low sheet resistance(2.18Ω/sq),good EMI shielding effectiveness(EMI SE of 48.1 dB),high mechanical strength(155.9 MPa),and overall toughness(19.4 MJ/m^(3)).Moreover,the excellent electrical conductivity and light absorption capacity of the MXene-PEDOT:PSS conductive layer mean that these Janus films display multi-source driven heating functions,producing excellent Joule heating(382℃ at 4 V)and photothermal conversion(59.6℃ at 100 mW/m^(2))properties.展开更多
As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic c...As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic characteristics of a piezoelectric energy harvesting system including a piezoelectric energy harvester, a bridge rectifier, and a storage capacitor. To accomplish this, this energy harvesting system is modeled, and the charging process of the storage capacitor is investigated by employing the in-phase assumption The results indicate that the charging voltage across the storage capacitor and the gathered power increase gradually as the charging process proceeds, whereas the charging rate slows down over time as the charging voltage approaches to the peak value of the piezoelectric voltage across the piezoelectric materials. In addition, due to the added electrical damping and the change of the system natural frequency when the charging process is initiated, a sudden drop in the vibration amplitude is observed, which in turn affects the charging rate. However, the vibration amplitude begins to increase as the charging process continues, which is caused by the decrease in the electrical damping （i.e., the decrease in the energy removed from the mechanical vibration）. This electromechanical coupling characteristic is also revealed by the variation of the vibration amplitude with the charging voltage.展开更多
力学性能尺寸效应是水泥基材料的一种自然现象。采用市售的三种加固灌浆料，分别测定端面尺寸为100 mm ×100 mm和150 mm ×150 mm 两种尺寸试件的立方体抗压强度、劈裂抗拉强度、棱柱体抗压强度、抗折强度和静压受力弹性模量...力学性能尺寸效应是水泥基材料的一种自然现象。采用市售的三种加固灌浆料，分别测定端面尺寸为100 mm ×100 mm和150 mm ×150 mm 两种尺寸试件的立方体抗压强度、劈裂抗拉强度、棱柱体抗压强度、抗折强度和静压受力弹性模量，各试件成型数量在30组以上，试验得出三种加固灌浆料的立方体抗压强度尺寸效应换算系数范围为0．81～0．87，平均值为0．84；劈裂抗拉强度换算系数范围为0．77～0．87，平均值为0．82；轴心抗压强度换算系数范围为1．0～1．03，平均为1．0；抗折强度换算系数范围0．82～0．88，平均为0．86；静压受力弹性模量尺寸效应系数范围为0．89～0．96，平均为0．92。抗压强度随着强度提高，换算系数降低，而弹性模量的规律相反。分析表明，与混凝土相比，加固灌浆料 C-S-H 凝胶体积含量高、骨料小、水胶比低是造成尺寸效应显著的原因。展开更多
Overrunning clutches are unidirectional drive mechanisms that are widely used in transmission systems.However,existing overrunning clutches have complex structures,require high preparation accuracy,and fail after a ce...Overrunning clutches are unidirectional drive mechanisms that are widely used in transmission systems.However,existing overrunning clutches have complex structures,require high preparation accuracy,and fail after a certain degree of wear.To address these issues,we propose a new type of overrunning clutch consisting of a conical structure and novel compression-torsion conversion(CTC)metamaterial with curved plates.Theoretical calculations are employed to guide the material distribution and ensure the deformation coordination of the curved-plate CTC metamaterial for greater ultimate torque.The transmission mechanism of the proposed overrunning clutch is derived to guide the parameter selection of the CTC metamaterial and the conical structure.Experiments and finite element simulations reveal that the curved-plate CTC metamaterial features excellent CTC efficiency,flexibility,and transverse stiffness,which is conducive reducing the resistance of the overrunning state and ensures stability during operation.The unidirectional transmission system constructed with the new overrunning clutch shows reliable performances under working and overrunning states.The constructed overrunning clutch provides an effective one-way transmission method.The clutch with simple construction and self-compensated ability for wear exhibits great potential in miniaturized and lightweight equipment or robots.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.51205302)the Fundamental Research Funds for the Central Universities,China(Grant No.K5051304011)
文摘Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezoelectric energy harvester （PEH） is usually designed as a linear resonator, and suffers from a narrow operating bandwidth. To achieve broadband energy harvesting, in this paper we introduce a concept and describe the realization of a novel nonlinear PEH. The proposed PEH consists of a primary piezoelectric cantilever beam coupled to an auxiliary piezoelectric cantilever beam through two movable magnets. For predicting the nonlinear response from the proposed PEH, lumped parameter models are established for the two beams. Both simulation and experiment reveal that for the primary beam, the introduction of magnetic coupling can expand the operating bandwidth as well as improve the output voltage. For the auxiliary beam, the magnitude of the output voltage is slightly reduced, but additional output is observed at off-resonance frequencies. Therefore, broadband energy harvesting can be obtained from both the primary beam and the auxiliary beam.
基金support for this work by the National Key Research and Development Program of China(No.2019YFA0706802)the National Natural Science Foundation of China(Nos.51903223 and 12072325)the National Natural Science Foundation of China of Henan Province(No.222300420541).
文摘The strategy of incorporating polymers into MXene-based functional materials has been widely used to improve their mechanical properties,however with inevitable sacrifice of their electrical conductivity and electromagnetic interference(EMI)shielding performance.This study demonstrates a facile yet efficient layering structure design to prepare the highly robust and conductive double-layer Janus films comprised of independent aramid nanofiber(ANF)and Ti3C2Tx MXene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)layers.The ANF layer serves to provide good mechanical stability,whilst the MXene/PEDOT:PSS layer ensures excellent electrical conductivity.Doping PEDOT:PSS into the MXene layer enhances the interfacial bonding strength between the MXene and ANF layers and improves the hydrophobicity and water/oxidation resistance of MXene layer.The resultant ANF/MXene-PEDOT:PSS Janus film with a conductive layer thickness of 4.4μm was shown to display low sheet resistance(2.18Ω/sq),good EMI shielding effectiveness(EMI SE of 48.1 dB),high mechanical strength(155.9 MPa),and overall toughness(19.4 MJ/m^(3)).Moreover,the excellent electrical conductivity and light absorption capacity of the MXene-PEDOT:PSS conductive layer mean that these Janus films display multi-source driven heating functions,producing excellent Joule heating(382℃ at 4 V)and photothermal conversion(59.6℃ at 100 mW/m^(2))properties.
基金Project supported by the National Natural Science Foundation of China(Grant No.10476019)the Fundamental Research Funds for the Central Universities(Grant No.K5051304011)
文摘As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic characteristics of a piezoelectric energy harvesting system including a piezoelectric energy harvester, a bridge rectifier, and a storage capacitor. To accomplish this, this energy harvesting system is modeled, and the charging process of the storage capacitor is investigated by employing the in-phase assumption The results indicate that the charging voltage across the storage capacitor and the gathered power increase gradually as the charging process proceeds, whereas the charging rate slows down over time as the charging voltage approaches to the peak value of the piezoelectric voltage across the piezoelectric materials. In addition, due to the added electrical damping and the change of the system natural frequency when the charging process is initiated, a sudden drop in the vibration amplitude is observed, which in turn affects the charging rate. However, the vibration amplitude begins to increase as the charging process continues, which is caused by the decrease in the electrical damping （i.e., the decrease in the energy removed from the mechanical vibration）. This electromechanical coupling characteristic is also revealed by the variation of the vibration amplitude with the charging voltage.
文摘力学性能尺寸效应是水泥基材料的一种自然现象。采用市售的三种加固灌浆料，分别测定端面尺寸为100 mm ×100 mm和150 mm ×150 mm 两种尺寸试件的立方体抗压强度、劈裂抗拉强度、棱柱体抗压强度、抗折强度和静压受力弹性模量，各试件成型数量在30组以上，试验得出三种加固灌浆料的立方体抗压强度尺寸效应换算系数范围为0．81～0．87，平均值为0．84；劈裂抗拉强度换算系数范围为0．77～0．87，平均值为0．82；轴心抗压强度换算系数范围为1．0～1．03，平均为1．0；抗折强度换算系数范围0．82～0．88，平均为0．86；静压受力弹性模量尺寸效应系数范围为0．89～0．96，平均为0．92。抗压强度随着强度提高，换算系数降低，而弹性模量的规律相反。分析表明，与混凝土相比，加固灌浆料 C-S-H 凝胶体积含量高、骨料小、水胶比低是造成尺寸效应显著的原因。
基金supported by the National Natural Science Foundation of China(Grant No.12172388).
文摘Overrunning clutches are unidirectional drive mechanisms that are widely used in transmission systems.However,existing overrunning clutches have complex structures,require high preparation accuracy,and fail after a certain degree of wear.To address these issues,we propose a new type of overrunning clutch consisting of a conical structure and novel compression-torsion conversion(CTC)metamaterial with curved plates.Theoretical calculations are employed to guide the material distribution and ensure the deformation coordination of the curved-plate CTC metamaterial for greater ultimate torque.The transmission mechanism of the proposed overrunning clutch is derived to guide the parameter selection of the CTC metamaterial and the conical structure.Experiments and finite element simulations reveal that the curved-plate CTC metamaterial features excellent CTC efficiency,flexibility,and transverse stiffness,which is conducive reducing the resistance of the overrunning state and ensures stability during operation.The unidirectional transmission system constructed with the new overrunning clutch shows reliable performances under working and overrunning states.The constructed overrunning clutch provides an effective one-way transmission method.The clutch with simple construction and self-compensated ability for wear exhibits great potential in miniaturized and lightweight equipment or robots.
