Search

Alpha Magnetic Spectrometer (AMS-02) is a particle-physics detector from a module attached to the outside of the International Space Station (ISS). The temperature of the components in AMS-02 must be kept within their different operational ranges but also must be stable over both time and volume. Thermal modeling and simulations for the radiator and the electronic crates of AMS-02 were carried out by applying the Crank–Nicholson implicit solution. Based on reducing the temperature gradient of the radiator and the mass of the thermal control system, the layout of the heat pipes in the radiator was optimized to solve the overheating issue of the electronic crates. The non-operational and operational temperature dissipation for the thermal control system was calculated. The analysis results for the radiator and the electronic crates can meet the running requirements of AMS-02 on the ISS. [ABSTRACT FROM AUTHOR]

Mechanical frequency up-conversion is a technique whereby a high-frequency oscillation is induced from a low-frequency source and aims to address inherent problems in low frequency vibration energy harvesting. This work presents a novel 1:2:6 internal resonances based frequency up-converting harvester in which the operation frequency is 6 times up-converted. Compared to traditional conceptual mechanisms (e.g. mechanical impact, mechanical plucking, impulsive acceleration), the proposed harvester can operate at much lower acceleration level, the missing of sound during the frequency conversion also reduces the energy consumption. Experimental measurements and theoretical simulations demonstrate that the proposed design can collect energy from ultra-low frequency (< 5 Hz) vibration sources. In addition, the harvester shows very high performance compared to the current state-of-the-art devices, a maximum 2.07 mW of average power is obtained from the fabricated prototype at the excitation frequency and level of 1.71 Hz & 0.19 g, respectively. [ABSTRACT FROM AUTHOR]

Piezoelectric stack actuators have been widely applied in mirco- or nano-positioning systems, but its hysteresis nonlinearity limits the performance. A driving power supply with charge feedback control was proposed to compensate the hysteresis of piezoelectric stack actuators. The drive circuit controlled by PWM waves was implemented in printed circuit board. A real-time controller was designed to acquire the voltage signals, calculate the charge on piezoelectric stack actuator and generate the PWM waves for drive circuit. Experimental results show that the proposed power supply with charge feedback control can effectively compensate the hysteresis and improve the positioning accuracy. [ABSTRACT FROM AUTHOR]

To overcome the drawbacks in the active and passive control systems, a low-powered semi-active approach based on synchronized switch damping techniques using piezoelectric materials have been developed. The synchronized switch damping (SSD) method, which consists in a nonlinear processing of the voltage on a piezoelectric actuator by switch control, is used to shift the phase and amplify the amplitude of the generated voltage on the piezoelectric element, which is helpful to enhance the energy conversion and control performance. In this paper, several new SSD control methods developed by the authors, including SSD control based on negative capacitance (SSDNC), and unsymmetrical SSD, are introduced. Moreover, two examples of application of SSD methods in aerospace engineering are given. Finally, the future directions of research in semi-active control are also summarized. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to investigate the effect of frictional materials and surface texture on the energy conversion efficiency and the mechanical output performance of the ultrasonic motor (USM).Design/methodology/approach A newly designed testing system was set up to measure the mechanical output performance of the USM. The influence of different frictional materials on the output performance of the USM was studied under the same assembly process and parameters. The surface texture was fabricated by laser ablation processing. The effects of surface texture and input parameters on the energy conversion efficiency and mechanical output performance of the USM were studied.Findings The results show that polyimide (PI) composites as frictional material can significantly improve the output performance of the USM compared to polytetrafluoroethylene (PTFE) composites. When the pre-load is 240 N, the energy conversion efficiency of the USM using textured PI composites as frictional material can reach 41.93 per cent, increased by 29.21 per cent compared to PTFE composites, and the effective output range of the USM is increased to 0.7-1.1 N m. Besides, the pre-load and surface texture have a great influence on the output performance of the USM.Originality/value PI composites can improve the mechanical output performance of the USM. Surface texture can also improve the interface tribological properties and the energy conversion efficiency based on the advanced frictional materials, which will contribute to the increment of the output performance of the USM under the same input conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The harvester can scavenge energy from ultra-low frequency vibrations. • The harvester can capture vibration energy from any direction. • The harvester can up-convert the excitation frequency through internal resonance. • The harvester is designed with a novel piezoelectric spring based on binder clips. • A significant generated power of 13.29 mW (at 0.26 g, 2.03 Hz) is obtained. Abstract Low frequency vibration is a ubiquitous energy existing in our environment, but a large efficient harvesting of which remains challenging. This paper presents a simple piezoelectric spring architecture based on a common binder clip structure. The harvester with pendulum spring allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric transducer. Due to the basic characteristics of spring pendulums, the proposed harvester can efficiently scavenge not only ultra-low frequency but also multi-directional vibrational energies. Modeling and design are conducted and a normalized expression of the harvester behavior is given. Chirp and human motion excitations are used to evaluate the proposed harvester's performances. Simulation and experimental results are in good agreement. The proposed device could generate a high output power (13.29 mW) at a low operating frequency (2.03 Hz), which shows great application prospects in the power supply of wearable products, ocean buoys, etc. [ABSTRACT FROM AUTHOR]

In view of low conductivity and thin layer structure of carbon fiber reinforced polymer (CFRP), the high frequency eddy current testing (HF-ECT) technique operating in the frequency range up to 100 MHz is considered to be better suited for this less conductive material. However, high frequency ECT method is more susceptible to various interference factors, causing many difficulties in the system construction and implementation. Concerning this issue, the feasibility of using low frequency ECT method for CFRP inspection was fully explored in this paper, and on this basis a high precision low frequency ECT system with the working frequency up to 250 kHz was developed. The system is mainly involving the small-size transmitter-receiver (T-R) type of probe, weak-signal extraction method using the lock-in amplifier and the C-scan imaging technique. The true skin depths of eddy current generated in unidirectional and orthogonal CFRP plates by small air-cored coil were calculated with 3D finite element simulation, thereby determining the high sensitivity of low frequency ECT for surface and near surface defects in CFRP. With the developed system, the direction of different fiber plies was successfully detected, and the location and size of different damages were also clearly visualized in the scan image. The proposed research can play a role of guiding the development of highly effective low frequency ECT method and detecting system for CFRP material. [ABSTRACT FROM AUTHOR]

An energy-based continuum damage mechanics model was employed to investigate the effect of drilling-induced delamination on tensile strength of carbon fiber-reinforced polymer laminates and the residual strength was predicted. The decrease in tensile strength caused by delamination was investigated in detail by a finite element method (FEM) model. Experiments were also conducted to validate the numerical results. The drilling-induced delamination was measured with ultrasonic C-scan technique and modeled as deletions of corresponding cohesive elements in the FEM model. Different sizes of delamination zones were investigated and the predicted strengths were compared with experimental results. The FEM model showed that the decrease in strength is mainly caused by early failures of outer plies. Good correlation between numerical simulations and experimental results was also obtained. [ABSTRACT FROM AUTHOR]

In semi-active synchronized switch damping (SSD) approaches for structural vibration control, the damping effect is achieved by properly switching the voltage on the piezoelectric actuators. Unsymmetrical SSD switch circuit has been designed in the previous paper to increase the effective voltage range on the PZT actuator for improvement of the control performance. In this study, analysis and experimental validation of control performance of a synchronized switch damping system based on the unsymmetrical switch circuit are carried out. First the model of an unsymmetrical SSD system is presented and the working principle is introduced. The general expression of the switched voltage on the piezoelectric actuator is derived. Based on its periodicity in steady-state control, the harmonic components of the actuator voltage are derived using Fourier series expansion. Next, the displacement response of the system is derived under combined actions of the excitation and switched voltage. Finally, a setup of a flexible beam with unsymmetrical switch circuit is used to demonstrate the control performance under different voltage sources and to verify the theoretical results. The results show that the control performance mainly depends on the voltage range on the PZT. A higher effective voltage range can be generated in unsymmetrical SSDV than in symmetrical SSDV and better control performance can be achieved at the same negative actuator voltage. The unsymmetrical SSDV makes better utilization of the actuator capability. [ABSTRACT FROM AUTHOR]

This paper presents a FEM model for the simulation of delamination in composite materials under fatigue loads using extended cohesive interface elements. A virtual fatigue damage variable is proposed to continually locate the crack tip elements with local element information only. The proposed method allows for a fully automatic identification of crack tip elements without any global information. Once crack tip elements are identified, the fatigue damage accumulation is determined by a modified Paris-law with a strain energy release rate correction method to reduce mesh sensitivity. The predicted delamination growth rates of different mesh sizes were compared with experimental results from open literature using a mode-I Double Cantilever Beam specimen and a mode-II 4-point End Notch Flexure specimen respectively. In all cases good agreement was obtained with weak mesh dependency. [ABSTRACT FROM AUTHOR]

Reconstruction of the nine stiffness coefficients of two different composites was implemented by inverting the measured Lamb waves phase velocities. The inversion was carried out through genetic algorithms (GAs) by minimizing the error between the calculated and the measured velocities. Forward problem of calculating phase velocities for a material properties individual in GAs was solved using a third-order shear deformation theory (ToSDT). Lamb wave propagation was visualized with a laser generation based imaging (LGBI) system which uses a laser source to generate ultrasonic waves. The experimental phase velocities were evaluated directly based on the position-time diagrams of Lamb waves. The nine stiffness coefficients were reconstructed using phase velocities of S 0 mode and A 0 mode measured along only three propagation directions. The reconstructed material properties were verified by comparing their corresponding theoretical velocities with the experimentally measured velocities. [ABSTRACT FROM AUTHOR]

Interface interactions between nanoparticles and polymer matrix have crucial effects on microstructures and properties. We demonstrate that polyurethane dielectric elastomer filled with titanium dioxide functionalized graphene, fabricated as a flexible micro-actuator, displays evident electric stimulus response and electric field induced strain. The hydrophilicity and wettability of graphene can be greatly enhanced by decorating nano-TiO 2 onto graphene, which causes the improved interface interactions between fillers and polymers. Higher dielectric constant, less loss modulus, elevated breakdown strength, and better electric stimulation responses of the novel titanium dioxide functionalized graphene–polyurethane dielectric elastomer composite are achieved due to enhanced filler–matrix interface. The maximum electric induced thickness strain of this titanium dioxide functionalized graphene–polyurethane dielectric elastomer composite is 72.4% at 38.7 V/μm, which is 1.8 times of the electric induced strain of graphene–polyurethane composite. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical and experimental analysis of broadband sound transmission control of an aluminum panel in the frequency range between 30 Hz and 1 kHz. Based on the analysis of characteristics of sensor-actuator pairs, piezoelectric patches bonded on the structure are used as actuators, and collocated accelerometers are used as sensors. Then a hybrid decentralized control law is derived, which has a broad control band and puts more control authority on the most sound radiation effective mode. This control law comprises two parts: one is the direct velocity feedback controller, and the other one, relatively new, is called the negative acceleration feedback (NAF) controller. The control architecture is decentralized, which means each controller works independently. Due to the second-order dynamic property of the NAF controller and the fact that the structure’s frequencies may shift, the Hilbert-Huang method is used for quick and automatic identification of the natural frequency. Finally, open loop and closed loop experiments are presented to support the theoretical analysis. The active control results demonstrate that the panel’s vibration level can be suppressed by 16.7 dB and the broadband sound pressure level could be lowered by more than 7 dB. [ABSTRACT FROM AUTHOR]

The electromechanical property of a diaphragm type actuator comprising a copper phthalocyanine oligomer noncovalent functionalized graphene-polyurethane dielectric elastomer (CuPc-RGO@PU) composite is described. The composite film had a dielectric constant of 102 with a dielectric loss of 0.13 at 3.0 wt% CuPc-RGO filler and 1k Hz. The composite film had a loss modulus of 195 MPa with a loss tangent of 0.4 at glass-transition temperature. At 37 MV/m, the electric field induced strain of CuPc-RGO@PU is more than 2.8 and 2.0 times higher than that of CuPc@PU and RGO@PU. The nanocomposites thus seem to be attractive for Micro-Electro-Mechanical System applications. [ABSTRACT FROM PUBLISHER]

With the rapid development of the aerospace industry, the control of aircraft structural vibration becomes increasingly important. Semi-active vibration control method based on synchronized switch damping have been attracted more attention due to its robustness compared with passive approaches and simplicity compared with active approaches. In this paper, three SSD semi-active control methods combined with a modal observer were applied to multimodal vibration suppression of an aircraft panel with stiffeners, and their effectiveness was verified by experimental results. A state observer was built based on the experimentally identified state-space model of the panel. Modal displacement of the panel was identified on line using the state observer and used in switch control of different piezoelectric actuators. Since the vibration characteristics of the panel with stiffeners was very complicated and its natural frequencies were distributed densely, use of the identified modal displacement as the reference signal for voltage switching in SSDI, SSDV and SSDNC improved the control effect for some specific modes and simplified the system. Good performances of vibration suppression were achieved in both single-mode control and multimodal control. [ABSTRACT FROM AUTHOR]

Abstract: Poly(methyl methacrylate)-functionalized graphene/polyurethane (MG–PU) dielectric elastomer composites were synthesized. MG was prepared by atom transfer radical polymerization (ATRP) and used as conducting filler. The microstructure of MG and MG–PU was characterized by SEM, TEM and XRD. The thermal degradation, mechanical, dielectric and electromechanical properties were investigated. The three-dimensional (3D) electric field induced displacement and strain of dielectric elastomer surface was observed and measured for the first time. Comparing with pure PU elastomer, the dielectric properties and electric field induced strain performance of MG–PU dielectric elastomer composites were significantly improved. The 1.50wt% MG–PU film had high relative permittivity and electric field induced strain of 28.21 and 32.8%, respectively. [Copyright &y& Elsevier]

Highlights: [•] The MPFs’ piezoelectric properties are lower than those of bulk ceramic counterpart. [•] The effect of geometrical shape is a main cause of the low-properties. [•] The effect of polarization also is the cause of the low-properties of the MPFs. [•] There is excellent agreement between the expected and experimental measurements. [ABSTRACT FROM AUTHOR]

Quaternary piezoelectric ceramics Pb(Ni1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–Pb(Zr0.3Ti0.7)O3–xZnO (PNN–PFN–PZT–xZ, x=0.0–0.08 in molar ratio) were prepared by the conventional mixed-oxide method. The effects of ZnO content on the microstructure and piezoelectric properties were systematically investigated. Increasing ZnO additive promotes the phase structure transformation from rhombohedral to tetragonal, indicating the presence of the morphotropic phase boundary in the ZnO-modified PNN–PFN–PZT system. The results show that ZnO doping significantly improves the coercive field (E c ), Curie temperature (T c ), and temperature stability (Δf r /f r 30°C, Δd 31/d 31 30 °C) of the PNN–PFN–PZT–xZ ceramics, although the piezoelectric constant (d 33, d 31) decreases slightly with increasing ZnO content. Taking into consideration the piezoelectric property and temperature stability, the obtained ceramic sample with x=0.04 exhibited favorable properties, which are listed as follows: d 33=810pC/N, k p =0.647, ε r =6243, tan δ=2.74%, E c =4.7kV/cm, and T c =136°C. [ABSTRACT FROM AUTHOR]

A hybrid model is proposed with the Prandtl-Ishlinskii operator and feedforward neural network. The hybrid model consists of three layers, where play operator is the transfer function of first layer. The training algorithm for model identification is derived from the backpropagation algorithm. With the measured data of piezoelectric actuator, a simulation is performed and shows that the hybrid model can precisely describe the asymmetric hysteresis loops. Incorporating the hybrid model into a feedforward controller, experiments indicate that the hybrid model exhibits a good performance for real-time control and the maximal tracking error is reduced by 76.75% with feedforawrd and PID controller. [ABSTRACT FROM AUTHOR]

(KNa)NbO piezoelectric ceramics can be sintered at a temperature as low as 750 °C for 5 h by incorporating LiCO + BiO + ZnO as the sintering aid, whereas the conventional sintering temperature is around 1,100 °C. The optimal 'soft' piezoelectric properties are obtained for ceramics sintered at 850 °C for 5 h. The dielectric permittivity ( ε), piezoelectric coefficient ( d), electromechanical coupling ( k) and mechanical quality factors ( Q) of (K, Na)NbO modified with 5.5 wt% sintering aids are 1,436, 90 pC/N, 0.3 and 10, respectively. These values are similar to the values obtained for (KNa)NbO ceramics sintered above 1,100 °C. The underlying mechanism for abrupt change of dielectric permittivity is explained. [ABSTRACT FROM AUTHOR]

Abstract: (K, Na)NbO3-based lead free materials have been found to exhibit good piezoelectric properties due to the orthorhombic–tetragonal polymorphic phase transition (PPT) temperature compositionally shifted downward to near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties. In this work, new quaternary (1−x) (K0.4425Na0.52Li0.0375)(Nb0.8925Sb0.07Ta0.0375)O3 (KNLNST)–xSrTiO3 (ST) lead-free piezoelectric ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were also studied. The results of X-ray diffraction reveal that SrTiO3 diffuses into the KNLNST lattices to form a new solid solution with a perovskite structure. After the addition of SrTiO3, tetragonal–orthorhombic phase transition shifts to lower temperatures. The good piezoelectric properties of 0.995 KNLNST–0.005 ST material were found to be d 33∼295pC/N, k p∼42%, and ε r∼1902, with greatly improved temperature stability over the temperature range of 0–100°C, demonstrating practical potential for actuator and ultrasonic transducer applications. [Copyright &y& Elsevier]

Aims at increasing the wing's lift and weakening the wing's shock wave, flow active control is studied by using the fluid mechanics. A new active control method based on piezoelectric elements is proposed, in which piezoelectric elements are buried on upper surface of winginduces periodic disturbance of boundary layer. The numerical simulation of the aerodynamic characteristics during the deformation process is done using the structural grid and the unsteady flow calculation method. The effect of piezoelectric elements on increasing the lift and weakening the shock of the aircraft wing is analyzed using computational fluid dynamics (CFD). Most previous studies were confined in a two-dimensional air-foil numerical simulation. In this article, its computing method is extended to a three-dimensional wing model to verify the validity of the new control method. Research shows that through appropriate parameter optimization, partial active deformation can improve the aerodynamic characteristics of airfoil. With the low roach number, the lift coefficient can be increased by 15% and the drag coefficient can be descended by 16%. The shock wave will move backward by control in the condition of high roach number and the lift coefficient of symmetrical airfoil can be improved by 17%. The self-adaptive wing can meet aerodynamic needs in variety of conditions. [ABSTRACT FROM AUTHOR]

This paper deals with eddy current testing simulation for carbon-fibre reinforced polymer composites (CFRPs) using an edge - element FEM code. The FEM code is based on the A formulation and it uses the coupled analysis with external fields. The coil impedance variations due to the fibre orientation and cracks in CFRP plates with unidirectional plies are computed. The conductivity of CFRP is characterized as low value and high anisotropy, which cause the distinct difference between CFRP and isotropic metal ECT signals. The correlation of the fibre orientation with coil impedance variations is obtained, but the exact fibre arrangement in a composite plate can't be ascertained because of signal symmetry. Another method for determining the fibre orientation via the edge effect is presented in this study. According to the numerical results, the shape of cracks in a CFRP plate is not easily evaluated from the detection signal curves unless the fibre orientation is perpendicular to the crack path. [ABSTRACT FROM AUTHOR]

K0.5Na0.5NbO3 (KNN) lead-free piezoelectric ceramics containing 1 mol% ZnO (KNNZ) were prepared by optimizing the sintering conditions using the newly developed K5.70Li4.07Nb10.23O30 (KLN) as a sintering aid. The phase structure and electrical properties of the KNNZ ceramics were investigated as a function of the KLN concentration. The results show that a small amount of KLN was incorporated into the lattice and formed a single-phase perovskite structure. The KLN modification lowered the phase transition temperature of the orthorhombic–tetragonal structure and increased the Curie temperature. Interestingly, an appropriate amount of KLN can simultaneously improve the sinterability of the KNNZ ceramics and the ferroelectric and piezoelectric properties. Good piezoelectric and dielectric properties (piezoelectric constant, d 33  =  131 pC/N; planar coupling coefficient, k p  =  0.42; dielectric constant, ϵ r  =  634; and mechanical quality factor, Q m  =  20) were obtained for the KNNZ ceramics doped with 1 mol% KLN. Therefore, KNNZ + 1.0 mol% KLN ceramics containing an appropriate amount of KLN are good candidate materials for the preparation of lead-free piezoelectric ceramics. [ABSTRACT FROM PUBLISHER]

Abstract: Two-step sintering was applied to manufacture a typical Li- and Ta/Sb-modified alkaline niobate-based lead-free piezoelectric ceramics. The sintering condition dependences of dielectric constants and piezoelectric properties were investigated. Under the optimal condition, dense specimens have an average grain size of approximately 5μm, and show good dielectric and piezoelectric properties. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics sintered under the condition “1130/10/1020/15” show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), and dielectric constant (ɛ), which are 281pC/N, 50% and 1500, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Furthermore, the KNLNST ceramics maintain relatively low dielectric loss over wide temperature ranges. The result indicates that the KNLNST ceramics sintered by two-step sintering exhibit good temperature stability. [Copyright &y& Elsevier]

Abstract: Lead-free (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 piezoelectric ceramics were prepared by the conventional sintering method. The effects of the Sb content on the phase structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 ceramics were investigated. The much higher Pauling electronegativity of Sb compared with Nb makes the ceramics more covalent. By increasing x from 0.05 to 0.09, all samples exhibit a single perovskite structure with an orthorhombic phase over the whole compositional range, and the bands in the Raman scattering spectra shifted to lower frequency numbers. The grain growth of the ceramics was improved by substituting Sb5+ for Nb5+. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p ), and dielectric constant (ɛ), which are 304pC/N, 48% and 1909, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Besides, the underlying mechanism for variations of the electrical properties due to Sb5+ substitution was explained in this work. [Copyright &y& Elsevier]

Abstract: In a structural system with piezoelectric actuators, the damping effect can be achieved by properly switching the voltage on the actuators. Semi-active synchronized switch damping (SSD) approaches are typical switched-voltage control methods, which have recently been a topic of active research. In this study, the energy conversion of a SSD control system with an arbitrary switching frequency is investigated theoretically and validated numerically. First the general expression of the switched voltage on the piezoelectric actuator is derived. The results show that maximum voltage magnitude is obtained on the piezoelectric actuator when piezoelectric is switched at every odd number of displacement extrema. Next the average converted energy per vibration cycle is derived for an arbitrary switching frequency. The results show that the efficiency of energy conversion is reduced drastically even if the switching frequency is slightly deviated from the optimal frequency. Finally numerical simulation and experiments were carried out to validate the theoretical results. [Copyright &y& Elsevier]

The 0.55Pb(Ni1/3Nb2/3)O3–0.45Pb(Zr0.3Ti0.7)O3 (0.55PNN-0.45PZT) ceramics were prepared by conventional solid state reactions. The effects of calcining temperature on the particle size and piezoelectric properties of 0.55PNN-0.45PZT piezoelectric ceramics were investigated. The particle size and crystallinity of 0.55PNN-0.45PZT ceramic powders are influenced by calcining temperature, and therefore the microstructure and final piezoelectric properties of 0.55PNN-0.45PZT are different. The highest piezoelectric properties (d 33 = 720pC/N, k p = 0.55. ϵ r = 6255) were observed at the sample fabricated from the powder calcined at 1100°C, which was attributed to the improved crystallinity and the homogeneous distribution of the particles. [ABSTRACT FROM PUBLISHER]

Abstract: Considering the spillover and harmonic effect in real active vibration control, a novel composite controller based on disturbance observer (DOB) for the all-clamped panel is presented. The single-mode of the piezoelectric panel can be regarded as a second-order system. The unmodeled error of the current controlled mode, harmonic effects, uncontrolled mode effects, etc., are regarded as the lumped disturbances which can be estimated by the DOB, and the estimated value is used for the feed-forward compensation design. Then, an optimal linear quadratic regulator (LQR) strategy is employed for the feedback design. In order to solve the difficulty of determining the weight matrices of LQR, a chaos optimization method based on logistic map is proposed. So the weight matrices can be tuned automatically. Combining with a new transient performance function, the optimal weight matrices can be obtained. The composite controller can effectively suppress the lumped disturbances of the all-clamped panel. Experiment comparisons with conventional LQR are given to verify the effectiveness of the proposed method. [Copyright &y& Elsevier]

Abstract: This paper presents a new self-powered vibration damping technique, which is an application of the enhanced synchronized switching harvesting technique. Compared with other self-powered vibration damping techniques, it not only shows its robustness (particularly facing environmental drifts), but also can harvest the energy and supply power to other electronic circuits, while does not simply dissipate the electrical energy. Experimental results show that a vibration damping of about 5dB is achieved as a result of energy harvesting, in good agreement with the theory. In addition, the vibration damping system can be not only self-powered, but also supply power to other electronic circuits. In other words, there is a good trade-off between energy scavenging and vibration damping. Along with experimental results demonstrating the effectiveness of the ESSH implementation, we discuss the design of a device aimed at bridging the gap between research in this area and practical application. [Copyright &y& Elsevier]

Abstract: The synchronized switch damping (SSD) approaches based on piezoelectric actuators have been successfully used in multimode vibration control of structures. By suppressing voltage inversion at some displacement extrema, the control performance of SSD approaches can be significantly improved. In this study, conversion of energy from mechanical to electrical in two-mode control is analyzed for different amplitude ratios and frequency ratios. The results show that the converted energy in two-mode control with voltage inversion at every extremum is smaller than the sum of the energies of the two modes in single-mode control, but the converted energy of the second mode in two-mode control may exceed that in single-mode control when the amplitude ratio of the second mode to the first mode is small enough. The influence of voltage threshold used to suppress voltage inversion on energy conversion of the system and each individual mode is also investigated. The converted energy of the first mode in two-mode control may be much larger than that in single-mode control when voltage inversion is suppressed suitably. The analytical results can successfully explain the phenomenon in the previous control experiments and can also be extended to multimode control. [Copyright &y& Elsevier]

This paper presents an approach for acousto-ultrasonic source (passive damage or impact) localization based on metal core piezoelectric fiber (MPF) rosettes. MPF is a new type piezoelectric ceramic device with small size and has high directivity to sense Lamb waves. The response of surface-bonded MPF sensors to Lamb-wave fields is explored theoretically and experimentally. The good directional properties of MPF are used to determine the direction of propagation of the acoustic waves by mounting three MPF sensors in a rosette configuration. Two suitably spaced rosettes are used to locate the source of the ultrasound by taking the intersection of the direction given by each rosette. The performance of the rosettes for source location is validated on an aluminum plate. [ABSTRACT FROM AUTHOR]

The intrinsic hysteresis behavior of piezoelectric material limits the tracking control accuracy of the actuators. This paper describes a tracking control method for piezoelectric actuators based on the combination of feedforward and feedback loops. The hysteresis of piezoelectric actuators is linearized in feedforward loop with an inverse hysteresis model based on a neural network. The number of parameters in the neural network based inverse model is relatively small and the parameters are easy to identify. The feedback loop is used to reduce the accumulated error produced by the inverse hysteresis model. The experimental results show that the accuracy is significantly improved in tracking control by using the combination of feedback and feedforward control. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new switch control strategy based on an energy threshold is proposed for the synchronized switch damping techniques in multimode control. This strategy is derived from the total converted energy of a synchronized switch damping (SSD) system in a given time window. Using the new strategy the voltage is inverted only at those extrema where the effective distance, which is proportional to the converted energy between two neighboring extrema, exceeds the threshold. The new switch control strategy is used in both the synchronized switch damping on inductor (SSDI) technique and the synchronized switch damping on voltage source (SSDV) technique, which are applied to the two-mode control of a composite beam. Their control performances are compared with those of the single-mode control and those of classical SSDI and SSDV techniques in two-mode control. The experimental results show that voltage inversion is prevented at some of the displacement extrema to increase the total converted energy, and exhibit better global damping effect than classical SSDI and classical SSDV, respectively. In single mode, the best control performance is achieved when the voltage is inverted at every extremum. But in multimodal control, the total converted energy in a given time window is increased and the control performance is improved when some extrema are skipped. [Copyright &y& Elsevier]

Abstract: In the paper, a vibration damping system powered by harvested energy with implementation of the so-called SSDV (synchronized switch damping on voltage source) technique is designed and investigated. In the semi-passive approach, the piezoelectric element is intermittently switched from open-circuit to specific impedance synchronously with the structural vibration. Due to this switching procedure, a phase difference appears between the strain induced by vibration and the resulting voltage, thus creating energy dissipation. By supplying the energy collected from the piezoelectric materials to the switching circuit, a new low-power device using the SSDV technique is proposed. Compared with the original self-powered SSDI (synchronized switch damping on inductor), such a device can significantly improve its performance of vibration control. Its effectiveness in the single-mode resonant damping of a composite beam is validated by the experimental results. [Copyright &y& Elsevier]

Abstract: The solid solutions in the system of Ca and Pb hydroxyapatite, Ca10− χ Pb χ HA (χ =0–10), were successfully synthesized by high-temperature mixing method (HTMM) at 200°C for 12h under hydrothermal conditions. The samples were characterized by X-ray diffraction, chemical analysis and electron microscopic observation, and the site of the metal ions in the solid solutions was analyzed with the Rietveld method. The lattice parameters of the solid solutions prepared by both of the methods didn’t vary linearly with Pb contents, and they have two turning points of 0.4 and 0.6 of Pb content. It was found that Pb ions in the solid solutions preferentially occupied the M (2) site in the apatite structure. HTMM gives Ca–Pb HA solid solutions much better crystallization. However, due to the formation of intermediate compound of Pb3O2(OH)2 in the Pb(NO3)2·4H2O solution before mixing with (NH4)2HPO4 solution at 200°C, HTMM causes the decrease of crystallization of the samples with high Pb content. [Copyright &y& Elsevier]

Abstract: BaTiO3 (BT) powders were synthesized by the hydrothermal method for fabricating lead-free barium titanate piezoelectric ceramics. The obtained powders were washed by distilled water and 0.01N acetic acid solutions separately, and utilized to obtain piezoelectric ceramics by traditional sintering. BT ceramics with the highest piezoelectric properties (d 33 value is over 190 pC/N) was obtained from the BT powder synthesized at 250°C and washed by acetic acid solution. The influence of washing method and sintering temperature on the piezoelectric properties of BT ceramics were studied. The reasons were investigated by comparing the properties of BT powders and their compacts sintered at different temperature. [Copyright &y& Elsevier]

The energy conversion efficiency (ECE) of a piezoelectric generator can be denoted by its effective electromechanical coupling coefficient (EECC), which depends only on the geometry parameters with a certain boundary conditions. To obtain the optimal energy-harvesting device, the Raleigh Method was utilized to establish the analysis model of circular piezoelectric composite diaphragms. Simply supported and clamped boundary conditions were considered. The relationships between the performance parameters (EECC and natural frequency) and the structural parameters (diametric ratio β and thickness ratio α) of piezoelectric composite diaphragms were figured out. Given the correlative material parameters and boundary conditions, the performance parameters with the structural parameters as variables can be worked out. The simulation results show that the optimal structural parameters of a composite diaphragm in the case of the simply supported and clamped boundary conditions are different. A simply supported diaphragm generator tends to achieve higher effective electromechanical coupling coefficient and lower natural frequency, and is more suitable for the applications of energy harvesting. [ABSTRACT FROM AUTHOR]

Abstract: Terfenol-D composites attract much attention recently due to their large magnetostriction, small eddy energy loss and large operation frequency bandwidth. Binder layer in the composite usually mechanically weakens the composite and reduces the effective properties. A typical kind of magnetostictive composite is composed of Rare Earth metallic compound powder, matrix material and resin binder. The binder, which is usually flexible and forms mechanically weak interface in the composite, inevitably influences the overall magnetostriction of composites. In this paper, a theoretical model was developed to treat a simple deformation case of this kind of mechanically weak interface, in which the flexible layer has low stiffness to withstand deformation but no de-bonding or cracking. An infinite magnetostrictive plane with a circular inclusion was considered, where the matrix and inclusion are all general magnetostrictive materials which can be modeled by the standard square constitutive relation of magnetostriction. The binder layer of a certain thickness was modeled as a set of springs with no thickness but with an equivalent stiffness. The mathematical formulation was brought into the complex variable framework. The magnetoelastic field was solved and the effective magnetostriction was explicitly obtained. Comparisons with experimental results were also presented. In terms of this analysis, the interfacial stiffness has significant influences on the overall magnetostriction of composite. Increasing the interfacial stiffness can lead to large magnetostriction of composites. The measure for improving the interfacial stiffness includes increasing the binder modulus and reducing its thickness. [Copyright &y& Elsevier]

We describe a novel magnetic force control method. The method employs a mechanical stress applied to a magnetostrictive material to control the attractive force between fixed and movable members of a magnetic circuit that includes a permanent magnet. The method has the advantage over electromagnet control that a constant force can be maintained without energy consumption. We discuss the variation of the magnetic force with compression of several magnetostrictive materials. The experimental results agree with theoretical predictions of magnetic force based on analysis of an equivalent magnetic circuit and the piezomagnetic properties of the magnetostrictive materials. [ABSTRACT FROM AUTHOR]

A magnetic force control device with composite laminate of a giant magnetostrictive material (GMM) and a piezoelectric material (PZT) is proposed. This magnetic force control is based on inverse magnetostrictive effect of the GMM, whereby variation of the magnetization in the GMM changed with a applied voltage on PZT is converted to that of magnetic force by the magnetic circuits. Because of the capacitive properties of the PZT, the device requires no electric energy hence generates no heat to maintain constant force. Furthermore compared with conventional electromagnets, the device is simple and easy to assemble. In this paper, the principle of the magnetic force control is presented and the static and dynamic characteristics of the device are examined. [ABSTRACT FROM AUTHOR]

A new magnetic force control method using giant magnetostrictive material (GMM) was proposed and its feasibility was confirmed in earlier studies by the authors. This new method is based on the inverse magnetostrictive effect and the magnetic force is controlled by changing the stress or strain in the magnetostrictive material. This method is expected to have lower heat generation and higher energy conversion efficiency compared to traditional methods, since a constant magnetic force can be maintained by merely applying a constant stress. In this study, the energy conversion efficiency of this method is investigated experimentally using a universal test machine. The input elastic energy was calculated from the stress-strain loading curve and the converted magnetic energy was estimated from the generated magnetic field. Since the elastic energy is strongly dependent on the history of the strain-stress loading curve, and the loading curve is affected by the applied magnetic field in the magnetostrictive material, it is important to optimize the bias magnetic field for maximum energy conversion efficiency. The relationships between the elastic modulus and the magnetic field were measured experimentally and the results show that the bias magnetic field must be carefully chosen to obtain high efficiency of energy conversion. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 8–15, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10026 [ABSTRACT FROM AUTHOR]

The main problem with Shape Memory Alloy (SMA) actuators is their slow response speed. Current SMA actuators work in tens of seconds though they can generate large force and displacement outputs. The objective of the research in this paper is to improve the response speed of SMA actuators to 10 milliseconds or less. SMA actuators are driven by thermal energy and their slow response is attributed to the inefficient heat transfer. To improve the response, direct Ohmic heating was used in the experiments. The SMA actuators used in this study are Ti-Ni-Cu columns of [ABSTRACT FROM AUTHOR]

Abstract: 0.55Pb(Ni1/3Nb2/3)O3–0.45Pb(Zr0.3Ti0.7)O3(PNN–PZT) ceramics with different concentration of xFe2O3 doping (where x =0.0, 0.8, 1.2, 1.6mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe2O3. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN–PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d 33 ~956 pC/N, the electromechanical coupling factor k p ~0.74, and the dielectric constant ε r ~6095 are achieved for the specimen with 1.2mol% Fe2O3 doping sintered at 1200°C for 2h. [Copyright &y& Elsevier]

Employing the laser ultrasonic system, information on fatigue evolution can be captured and explicitly stored in the frequency‐wavenumber wavefield of the guided wave. This paper presents a deep‐learning architecture for processing the frequency‐wavenumber wavefield, which comprises two distinct steps: fatigue characterization and evolution prediction. Firstly, the fatigue characterization step employs a convolutional autoencoder (CAE) for compressing the frequency‐wavenumber wavefield and a fully connected network (FCN) for obtaining the fusion fatigue characteristic. Due to the high cost of experimental samples, extensive simulation‐generated wavefields are used to pre‐train the network. Subsequently, the fatigue evolution prediction model based on the latent ordinary differential equation (Latent‐ODE) is trained for the step‐by‐step prediction of fatigue evolution with a small amount of composite fatigue test data. The results validate the effectiveness of the deep‐learning architecture in characterizing fatigue and predicting its evolution, as well as the feasibility of the frequency‐wavenumber wavefield compression of guided wave. Highlights: The deep‐learning architecture for fatigue evaluation and prediction is proposed.The frequency‐wavenumber wavefield of guided wave is fused for fatigue evaluation.The fatigue evolution prediction is achieved using the Latent‐ODE model.The fatigue life of the composite specimen is predicted. [ABSTRACT FROM AUTHOR]

This paper proposes a modified theory for synthesizing the acoustic impedance of an absorbing panel by considering the interference among parallel absorbers. The absorbing panel comprises periodically distributed absorbers with different acoustic characteristics, and the periodic distribution allows the impedance of the panel to be characterized by that of a unit cell. However, at frequencies between the resonances of the absorbers in the unit cell, the unit-cell impedance given by traditional theory deviates significantly from that given by a finite-element model. Inspecting the flow field near the surface of the unit cell reveals that the out-of-phase flow plays an important role in the interaction among the parallel absorbers and induces the deviation. A modified theory is proposed by multiplying the original resultant impedance by a factor that considers the interaction. The modified theory is verified by numerical results for several typical absorbing panels with different patterns of unit cells and different geometrical parameters of absorbers, and experimental validation is also carried out. As further evidence for the correctness and universality of the modified theoretical model, a comparison is presented with the mutual-radiation-impedance theoretical model based on a Helmholtz resonator array panel. The results of validation on different absorbing panels and the comparison with the mutual-radiation-impedance method show that the modified theoretical model is better at predicting the absorption coefficient than is the traditional theory. [ABSTRACT FROM AUTHOR]

In the nondestructive evaluation for components of key equipment, sizing of natural crack is important in order to guarantee both the safety and efficient operation for large mechanical systems. Natural cracks have complex boundary and there may be electric current flowing through crack faces. If a simple model of artificial notch is used to simulate it, errors often occur in crack depth reconstruction from eddy current testing (ECT) signals. However, if a complex crack conductivity model is used, quantitative evaluation of natural crack will be transformed into a multivariable nonlinear optimization problem and the solution is difficult. In this paper, based on the relationship between crack parameters and features of multi-frequency ECT signals, a multi-output support vector regression algorithm using domain decomposition for parameters was proposed. The algorithm realized the quantitative evaluation of multiple parameters of crack in turn. Numerical examples with simulated and measured ECT signals were presented to verify the efficiency of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper examines the influence of pole and slot combinations on the electromagnetic performance of the flux-switching permanent magnet (FSPMs) machine. For this purpose, first the production of air gap flux density in machine analytically discussed. Next, five different pole and slot combination are selected by using the knowledge of air-gap flux density expression. The performances of the different combinations are analyzed and compared using the finite element analysis (FEA), and optimal pole and slot combination is suggested. It is found that the pole and slot combination has a dominant effect on machine performance and needs to be considered during the design stage. [ABSTRACT FROM AUTHOR]

Better understanding of the characteristics of the traveling wave and three-dimensional trajectory related to motion on the surface of the stator is very important for the design and performance improvement of the ultrasonic motors. In this paper, an accurate finite element model of a single stator with a fully coupled piezoelectric layer was established at a moderate computational cost. The finite element model was verified by experimental test at the inverse resonance point. Based on this model, the traveling wave and three-dimensional trajectory of stator surface, including the influence of the input voltage on the phase and amplitude of the displacements in three directions, are investigated. The results show that the trajectory of particles on the stator surface is an ellipse in three-dimensional space due to the phase differences between the three components of displacement in the radial, circumferential and axial directions. The amplitude of radial displacement is about 39.5% of that in the circumferential displacement, which should not be neglected. [ABSTRACT FROM AUTHOR]