Table of contents

Experimental modal analysis is of great importance for the dynamic characterization of structures. Existing methods typically employ out-of-plane forces for excitation and measure the acceleration or strain for modal analysis. However, these methods encountered difficulties in some cases. In this work, we proposed an in-plane excitation method based on thickness-shear (d₁₅) piezoelectric transducers. Through the combination of distributed d₁₅ PZT strips, arbitrary vibration modes can be selectively excited in a wide frequency range. Both simulations and experiments were conducted and the results validated the proposed method. Specifically, bending, torsional, and longitudinal vibration modes of a rectangular bar were selectively excited. Torsional modes of a shaft were excited without the aid of brackets and bending modes of a circular plate were excited with actuators placed at nodal lines. Furthermore, the electromechanical impedance of the PZT-structure system was measured from which the natural frequency and quality factor were directly extracted. Due to its simplicity and flexibility, the proposed vibration excitation method is expected to be widely used in near future.

We recorded a permanent phase transmission grating on a thin film made by using a recently developed holographic photomobile mixture. The recorded grating pitch falls in the visible range and can be optically manipulated by using an external coherent or incoherent low power light source. When the external light source illuminates the grating the entire structure bends and, as a consequence, the optical properties of the grating change. This peculiarity makes it possible to use the recorded periodic structure as an all-optically controlled free standing thin colour selector or light switch depending on the source used to illuminate the grating itself. Additionally, it could open up new possibilities for stretchable and reconfigurable holograms controlled by light as well as thin devices for optically reconfigurable dynamic communications and displays.

Kinetic façade systems can adjust to different environmental conditions, thereby improving daylight performance in buildings. Bistable laminates present large deflections and can maintain their state without continuous energy supply, appealing features for kinetic applications. Nevertheless, these engineered materials have yet to be studied for their potential for improving daylight performance in buildings. This study sought to test the daylight performance of a kinetic bistable screen using a case study approach that combines experimental testing and building performance simulation. This paper details research to design and fabricate the shading screen and the experimental testing of the screens' daylight performance. First, we focus on the design of a holder mechanism, which relies on a string system and shape memory alloys that actuate bistable flaps. Second, we experimentally collect data on daylight performance and compare it to simulation data to validate a daylight model. Results show that the designed bistable screen can increase the hours of adequate daylight throughout the year versus baseline cases, particularly when oriented south and east. The study suggests that bistable kinetic screens can help improve daylight performance in buildings.

This study aims at introducing a number of two-dimensional (2D) re-entrant based zero Poisson's ratio (ZPR) graded metamaterials for energy absorption applications. The metamaterials' designs are inspired by the 2D image of a DNA molecule. This inspiration indicates how a re-entrant unit cell must be patterned along with the two orthogonal directions to obtain a ZPR behavior. Also, how much metamaterials' energy absorption capacity can be enhanced by taking slots and horizontal beams into account with the inspiration of the DNA molecule's base pairs. The ZPR metamaterials comprise multi-stiffness unit cells, so-called soft and stiff re-entrant unit cells. The variability in unit cells' stiffness is caused by the specific design of the unit cells. A finite element analysis (FEA) is employed to simulate the deformation patterns of the ZPRs. Following that, meta-structures are fabricated with 3D printing of TPU as hyperelastic materials to validate the FEA results. A good correlation is observed between FEA and experimental results. The experimental and numerical results show that due to the presence of multi-stiffness re-entrant unit cells, the deformation mechanisms and the unit cells' densifications are adjustable under quasi-static compression. Also, the structure designed based on the DNA molecule's base pairs, so-called structure F‴, exhibits the highest energy absorption capacity. Apart from the diversity in metamaterial unit cells' designs, the effect of multi-thickness cell walls is also evaluated. The results show that the diversity in cell wall thicknesses leads to boosting the energy absorption capacity. In this regard, the energy absorption capacity of structure 'E' enhances by up to 33% than that of its counterpart with constant cell wall thicknesses. Finally, a comparison in terms of energy absorption capacity and stability between the newly designed ZPRs, traditional ZPRs, and auxetic metamaterial is performed, approving the superiority of the newly designed ZPR metamaterials over both traditional ZPRs and auxetic metamaterials.

Of all the smart materials that can vary with a change in external excitation, magnetorheological gel (MRG) is one of the most pre-eminent composites, having controllable and reversible responses according to the magnitude of the external magnetic field. Temperature has been identified as another important driver that can alter the dynamic properties of a MRG, and so far this has not been studied systematically. The temperature-dependent dynamic properties of a MRG under different magnetic field strengths were investigated by three kinds of experiments—strain amplitude, frequency and magnetic field sweep tests. The experimental results demonstrate that the storage and loss moduli of MRGs display a temperature-induced stiffening effect with a magnetic field but a temperature-induced softening effect in the absence of a magnetic field. The storage modulus improves with magnetic field strength, whereas the loss modulus first shows rapid growth and then a gradual reduction with increasing magnetic field strength. This temperature dependence of dynamic properties is also interpreted through different mechanisms related to the transformation of the MRG microstructure. Furthermore, a modified magnetic dipole model which could predict the relationship between storage modulus and magnetic field strength is combined with the classical Arrhenius equation expressing the effect of temperature on viscosity to describe the temperature dependence of the storage modulus of a MRG under different magnetic field strengths. This paper may provide some useful guidance for designing a magnetorheological device.

Multi-stable configurations of piezoelectric harvester are quite successful in achieving the two important goals, the broadband frequency response and large orbit oscillations exhibiting periodic, multi-periodic, and chaotic solutions. However, in the quest of achieving large amplitude broadband frequency response, assessment of induced strain levels considering the limits on the strain in piezoelectric material has received minimal attention. In this context, the investigation presents analytical formulation for the assessment of induced strain and voltage(s) in piezoelectric unimorph and bimorph cantilevers. The formulation quantifies not only the induced voltages in individual piezoelectric layers of a bimorph, but also the equivalent voltages in parallel and series connection modes, respectively. Also, while computing the induced voltage in the first piezoelectric layer, the contribution from the induced voltage of second piezoelectric layer to the acting bending moment is captured in the formulation. The formulations are validated through the experiments and results from the literature. Further, we have applied two practically useful normalization schemes, the $t_{p}$- and $t_{t}$-normalizations to the analytical expressions. Using the two normalization schemes, influences of variation of substrate and adhesive layer thicknesses, elastic moduli of layers, and substrate-to-composite length fraction are visualized and discussed. Based on the results, summarized guidelines for design and selection of geometric and material parameters are presented, which may also be applicable for other sensing and actuation applications. At last, practically suitable ranges and optimum values for the normalized design variables are proposed.

Fluidic artificial muscles (FAMs) are a popular actuation choice due to their compliant nature and high force-to-weight ratio. Variable recruitment is a bio-inspired actuation strategy in which multiple FAMs are combined into motor units that can be pressurized sequentially according to load demand. In a traditional 'fixed-end' variable recruitment FAM bundle, inactive units and activated units that are past free strain will compress and buckle outward, resulting in resistive forces that reduce overall bundle force output, increase spatial envelope, and reduce operational life. This paper investigates the use of inextensible tendons as a mitigation strategy for preventing resistive forces and outward buckling of inactive and submaximally activated motor units in a variable recruitment FAM bundle. A traditional analytical fixed-end variable recruitment FAM bundle model is modified to account for tendons, and the force–strain spaces of the two configurations are compared while keeping the overall bundle length constant. Actuation efficiency for the two configurations is compared for two different cases: one case in which the radii of all FAMs within the bundle are equivalent, and one case in which the bundles are sized to consume the same amount of working fluid volume at maximum contraction. Efficiency benefits can be found for either configuration for different locations within their shared force–strain space, so depending on the loading requirements, one configuration may be more efficient than the other. Additionally, a study is performed to quantify the increase in spatial envelope caused by the outward buckling of inactive or low-pressure motor units. It was found that at full activation of recruitment states 1, 2, and 3, the tendoned configuration has a significantly higher volumetric energy density than the fixed-end configuration, indicating that the tendoned configuration has more actuation potential for a given spatial envelope. Overall, the results show that using a resistive force mitigation strategy such as tendons can completely eliminate resistive forces, increase volumetric energy density, and increase system efficiency for certain loading cases. Thus, there is a compelling case to be made for the use of tendoned FAMs in variable recruitment bundles.

This work demonstrates that magnetoelectric composite heterostructures can be designed at the length scale of 10 µms that can be switched from a magnetized state to a vortex state, effectively switching the magnetization off, using electric field induced strain. This was accomplished using thin film magnetoelectric heterostructures of Fe_81.4Ga_18.6 on a single crystal (011) [Pb(Mg_1/3Nb_2/3)O₃]_0.68-[PbTiO₃]_0.32 (PMN-32PT) ferroelectric substrate. The heterostructures were tripped from a multi-domain magnetized state to a flux closure vortex state using voltage induced strain in a piezoelectric substrate. FeGa heterostructures were deposited on a Si-substrate for superconducting quantum interference device magnetometry characterization of the magnetic properties. The magnetoelectric coupling of a FeGa continuous film on PMN-32PT was characterized using a magneto optical Kerr effect magnetometer with bi-axial strain gauges, and magnetic multi-domain heterostructures were imaged using x-ray magnetic circular dichroism—photoemission electron microscopy during the transition to the vortex state. The domain structures were modelled using MuMax³, a micromagnetics code, and compared with observations. The results provide considerable insight into designing magnetoelectric heterostructures that can be switched from an 'on' state to an 'off' state using electric field induced strain.

An experimental proof of concept of a new semi-passive nonlinear piezoelectric shunt absorber, introduced theoretically in a companion article, is presented in this work. This absorber is obtained by connecting, through a piezoelectric transducer, an elastic structure to a resonant circuit that includes a quadratic nonlinearity. This nonlinearity is obtained by including in the circuit a voltage source proportional to the square of the voltage across the piezoelectric transducer, thanks to an analog multiplier circuit. Then, by tuning the electric resonance of the circuit to half the value of one of the resonances of the elastic structure, a two-to-one internal resonance is at hand. As a result, a strong energy transfer occurs from the mechanical mode to be attenuated to the electrical mode of the shunt, leading to two essential features: a nonlinear antiresonance in place of the mechanical resonance and an amplitude saturation. Namely, the amplitude of the elastic structure oscillations at the antiresonance becomes, above a given threshold, independent of the forcing level, contrary to a classical linear resonant shunt. This paper presents the experimental setup, the designed nonlinear shunt circuit and the main experimental results.

The different pre-structure formed by the particles determine the performance of magnetorheological elastomers (MREs). In this study, spherical cobalt particles with a diameter of 2–5 μm and chain-like cobalt particles (CCPs) composed of spherical particles with a diameter of about 1 μm with a chain length of 10–40 μm were respectively prepared. These two kinds of particles were used to prepared MREs under different orientation magnetic fields. The effects of different chain-like microstructures on the performance of MRE are compared. The dynamic viscoelastic test results of MREs show that the chain-like particles increased the movement resistance in the matrix, thereby increasing the damping factor of CCP-MREs. The special chain-like particles improved the Payne effect factor and magnetic field-induced storage modulus of isotropic CCP-MRE. It is worth noting that the performance of anisotropic CCP-MRE is different from traditionally believed performance improvement. Based on this work, a relationship curve between the MR effect and the adjacent particles' distance was proposed.

Shape memory polymer foam (SMPF) is being studied extensively as potential aerospace materials as they have high compression ratio, high specific strength and high specific modulus compared to other shape memory polymers. In this paper, a composite foam with shape memory epoxy as matrix and polyurethane as functional phase was prepared. The SMPF has been characterized by different analytical and testing methods, and its chemical crosslinking reaction and material properties have been studied. The SMPF was installed in the shape memory polymer composite (SMPC) flexible solar array system (SMPC-FSAS), and ground environment tests and orbital validation were performed. Considering the particularity of space environment, the thermal performance test of ground space environment can effectively test the reliability of shape memory performance. Finally, the SMPC-FSAS carried on SJ-20 satellite successfully deployed on geosynchronous orbit for the first time in the world. Moving forward, SMPF assesses the feasibility of applications in the space field and provides more valuable information.

Low-speed wind energy has potential to be captured for powering micro-electro-mechanical systems or sensors in remote inaccessible place by piezoelectric energy harvesting from vortex-induced vibration. Conventional theory or finite-element analysis mostly considers a simple pure resistance as interface circuit because of the complex fluid-solid-electricity coupling in aeroelastic piezoelectric energy harvesting. However, the output alternating voltage should be rectified to direct voltage to be used in practical occasions, where the theoretical analysis and finite-element analysis for complex interface may be cumbersome or difficult. To solve this problem, this paper presents an equivalent circuit modeling (ECM) method to analyze the performance of vortex-induced energy harvesters. Firstly, the equivalent analogies from the mechanical and fluid domain to the electrical domain are built. The linear mechanical and fluid elements are represented by standard electrical elements. The nonlinear elements are represented by electrical non-standard user-defined components. Secondly, the total fluid-solid-electricity coupled mathematical equations of the harvesting system are transformed into electrical formulations based on the equivalent analogies. Finally, the entire ECM is established in a circuit simulation software to perform system-level transient analyses. The simulation results from ECM have good agreement with the experimental measurements. Further parametric studies are carried out to assess the influences of wind speed and resistance on the output power of the alternating circuit interface and the capacitor filter circuit. At wind speed of 1.2 m s⁻¹, the energy harvester could generate an output power of 81.71 μW with the capacitor filter circuit and 114.64 μW with the alternating circuit interface. The filter capacitance is further studied to ascertain its effects on the stability of output and the settling time.

The intra-cellular wave dynamics of a water jetted phononic plate are experimentally investigated by means of high-resolution three-dimensional (3D) scanning laser Doppler vibrometry. The study is focused on the vibrational behavior around the ultra-wide bandgap of the plate (with a relative bandgap width of 0.89), as the critical frequency range of its phononic functionality. Broadband vibrational excitations are applied using a piezoelectric transducer and both in-plane and out-of-plane operational deflection shapes of the unit-cells are analyzed with respect to mode shapes calculated by finite element (FE) simulation. Attenuation and resonance of both symmetric and antisymmetric wave modes are validated, and it is shown that despite the absence of in-plane wave energy actuation, the symmetric modes are effectively excited in the phononic lattice, due to mode conversion from co-existing antisymmetric modes. Supported by FE modal analysis, this mode conversion observation is explained by the slight through-the-thickness asymmetry introduced during manufacturing of the phononic plate which leads to coupling of modes with different symmetry. The results confirm the potential of such detailed 3D inspection of phononic crystals (and in general acoustic metamaterials) in gaining full insight about their intracellular dynamics, which can also illuminate discrepancies with respect to idealized numerical models that might be due to manufacturing imperfections.

Tactile sensing plays a crucial role in robot manipulation, robot interaction, and health monitoring. Because of high sensitivity, simple structure, and superior interference immunity, optical tactile sensors based on optical imaging or optical conduction have been one of the most active research. Herein, a novel liquid lens-based optical sensor (LLOS) is presented. Different with existed optical tactile sensors, the main body of the proposed sensor belongs to a variable-focus optical lens with a liquid-membrane structure, and its focal length is changed with the contact force, thereby changing the propagation direction of light and affecting the perceived light intensity of the photosensitive element. By conducting some testing experiments, the LLOS demonstrates fast response (about 0.021 s), stable dynamic response characteristics, and good linearity (R-squared is about 0.99), repeated measurement accuracy (<0.006 V), and measurement accuracy (<0.2 N). Hence, the LLOS provides a new and promising method to measure tactile and has potential application in robotics nondestructive grasping and interactive input devices.

This paper proposes a mathematical model of the cavitation behavior to occur in a single-ended magnetorheological (MR) damper (MRD), and the effectiveness of the model is validated through the comparison with experimental results. Several causes of the cavitation behavior of MRD are discussed with different conditions of the initial pressure of the gas chamber and the piston stroke speed. The model to capture the cavitation behavior is then formulated considering differential equations for gas volume, internal pressure, ideal gas law, and bulk modulus of MR fluid. To calculate the flow rate, which is difficult to solve from the differential equations, the model is approximated as a nondimensional equation the parameters of the yield stress and pole length. Subsequently, the field-dependent damping force of MRD is computed using the gaseous cavitation model and nondimensional equation. To validate the proposed cavitation model, a single-ended MRD is designed, manufactured, and tested. It is observed that the damping force characteristics under cavitation are revealed to be much different from those under regular operation without cavitation. More specifically, it is hard to calculate the dissipation energy and hysteretic damping due to highly nonlinear characteristics with respect to the stroke and velocity. However, the proposed model can fairly capture the cavitation behavior showing an excellent agreement between simulation and experiment. In this work, to confirm the internal influence of MRD by cavitation, which is difficult to confirm experimentally, the changes of the pressure distribution and the gas-to-liquid volume ratio are analyzed through the simulation of the nondimensional equation. In addition, the bubbles representing the cavitation behavior are visually observed from the lower chamber of MRD.

An ionic polymer metal composites (IPMC) is a soft actuator that consists of an ionomer membrane, neutralized by mobile counterions and plated by metal electrodes. Despite their early promise in robotics, medical devices, and microsystem technologies, widespread application of IPMC actuators is far from being reached. Recent advancements in additive manufacturing technologies have the potential to expand the reach of IPMCs by affording the realization of complex, design-specific geometries that were impossible to attain with standard manufacturing techniques. For this potential to be attained, it is critical to establish physically-based models that could inform 3D printing, beyond the flat, thin, non-tapered geometries that have been the object of investigation for almost three decades. Here, we bridge this gap by presenting an analytical framework to study actuation of a double-clamped IPMC arch under an applied voltage. We adopt a thermodynamically the consistent continuum model to describe the coupled electrochemo-mechanical phenomena taking place within the IPMC. We establish an analytical solution for the electrochemistry using the method of matched asymptotic expansions, which is, in turn, utilized to compute osmotic pressure and Maxwell stress. The mechanical response of the IPMC arch is modeled as a plane strain problem with an induced state of eigenstress, which is solved with the use of a smooth Airy function. The accuracy of our analytical solution is validated through finite element simulations. Through a parametric analysis, we investigate the effect of curvature on the deformation and the reaction forces exerted by the clamps. The proposed analytical framework offers new insight into the response of curved IPMCs, in which progress on 3D printing should be grounded.

Broadening the bandwidth of vibration energy harvesters is a critical issue for their practical implementations. Although utilizing multi-degree-of-freedoms is a frequently used solution to widen the operating frequency range, the resultant effective bandwidth could consist of discrete peaks (existing local minimum points lower than the half-power level) if the modal amplitudes have large differences at different frequencies. To solve these problems, we designed a new electromagnetic multi-modal energy harvester, which works in a broad and continuous low-frequency bandwidth. This is achieved by attaching the magnet and the coil to a compliant frame integrated with two different kinked beams, respectively. In this way, the voltage can be generated in a continuous and wide frequency range by adjusting the amplitudes and phases of the magnet and the coil in different modes according to a proposed design requirement. Finite element results and experimental results are in good agreement with each other, which validate the performance of the proposed harvester. The experimental results demonstrate that the half-power bandwidth can be achieved in the range of 15.0 Hz and the maximum peak power is 1.56 mW at the center frequency of 40.5 Hz under base excitation of the root-mean-square acceleration of 0.24 g. The broadband and high power density feature are also validated in a random excitation test, so that this harvester has great potential for practical applications.

In this research, a new method based on singular spectrum analysis (SSA) and fuzzy entropy is developed for damage detection on thin wall-like structures, and the normalized fuzzy entropy is employed as an indicator to identify the severity of the damage. The lead zirconate titanate (PZT) transducers are used in this research to generate and detect the Lamb waves. During the detection, the collected signals from the PZT sensors are firstly decomposed and reconstructed by SSA to extract the feature of the damage, and then the reconstructed signals with the feature of the damage are processed to obtain the normalized fuzzy entropy. An experimental setup of an aluminium plate with added magnets is fabricated to validate the proposed method. The experimental results show that when magnets are attached on the aluminium plate, the normalized fuzzy entropy is smaller than that when there are no magnets. That is because when magnets are placed on the plate, the movement and some vibration modes of Lamb waves are disturbed by the added magnets and this disturbing effect can be enhanced by increasing the number and locations of the added magnets, and eventually the complexity and nonlinearity of the waves are weakened. The experimental results of a single damage with different number of magnets indicate that the normalized fuzzy entropy decreases linearly as the number of the added magnets increases, which demonstrates that the proposed method can be used to detect the severity of the damage. Moreover, the experimental results of multi-damage on different locations indicate that the normalized fuzzy entropy is relevant with both the total number and locations of the added magnets. The normalized fuzzy entropy decreases linearly as the total number of the magnets increases, and the entropy of a single damage is smaller than that of the multi-damage with the same total number of magnets, which demonstrates that the proposed method also can be used for multi-damage detection on a thin plate. This study provides us a new approach to identifying a single or multiple damages on thin wall-like structures.

A microfluidic chip, in which both the coil heater and the fluidic channel are designed in a 3D iterative structure, is developed and experimentally demonstrated. Using the empty surrounding 3D space, the microfluidic chip increases the heat transfer area, thereby increasing the fluid temperature by 51.3%, with the same power consumption, compared to heaters and channels typically designed on a 2D plane. After casting polydimethylsiloxane (PDMS) into a sacrificial mold printed using a 3D printer and dissolving the mold, the 3D coil Joule heater is fabricated by filling the interior part of the coil with liquid gallium by vacuuming. By adding an insulation wall filled with air having low thermal conductivity, an additional heating of 8.7% is achieved; this demonstrates the advantage of the 3D-printed soluble-mold technique, which can allow faster prototyping than the typical microfabrication based on soft lithography. Thus, this technique enables convenient design modifications with high priority for performance improvement. As all the components are manufactured simultaneously within a biocompatible, single PDMS body (because of the absence of bonding process between the devices), the risk of leakage in the device is inherently avoided, and the device can be bent without causing any fracture. Therefore, the reported fabrication process and devices are expected to contribute to miniaturization and performance enhancement of microfluidics; this will lead to the development of wearable 3D lab-on-a-chip devices in future.

In this study, 'three-dimensional structure' nanohybrid particle (SiO₂-GO) were synthesized by in situ hydrolysis and composited with perfluorosulfonic acid (PFSA) to increase the water uptake (WUP) and ion exchange capacity (IEC) of the cast membranes. Ionic polymer metal composite (IPMC) soft actuators were fabricated based on the cast pure PFSA, GO/PFSA and SiO₂-GO/PFSA membranes. The morphology and properties of IPMC were researched, and the relationship between them was analyzed in this article. The mechanism of SiO₂-GO particles enhancing the properties of IPMC was revealed. The effects of incorporating GO and SiO₂-GO on IPMC actuators were analyzed using physicochemical and electromechanical measurements comparing with the corresponding behavior of pure PFSA-based IPMC actuators. Morphology of IPMC showed effective incorporation of GO and SiO₂-GO and clarified the dependency of Pt interface electrode on the SiO₂-GO content of the PFSA membranes. The addition of SiO₂-GO increased dramatically the WUP and IEC of the PFSA membranes and autuation performance of the IPMC actuators. The IPMC with 1 wt% SiO₂-GO showed superb properties. The displacement of 1 wt% SiO₂-GO under 3 V AC voltage reached 28.4 mm, which is 3.2 times higher than that of the pure PFSA. The maximum displacement under DC voltage reached 44.7 mm (5.5 V), and the blocking force reached 43.2 mN (5 V), which increased respectively 1.1 times and two times.

The Inertial Confinement Fusion (ICF) targets are hollow glass microspheres with strong viscosity, easy agglomeration, small diameter, and fragile structure. The size and morphology of the ICF target are crucial to the success of ICF experiment. To obtain qualified targets, the manual detection method and automatic detection systems are mainly employed. However, hard contact existed between the targets and the manipulation platform in both methods, which may cause target damage. To solve this issue, a novel multi-mode piezoelectric acoustofluidic manipulation device is proposed to achieve the non-contact manipulation of sub-millimeter size ICF targets during detection process. The proposed device mainly consists of a disk-shaped container and a four-transducer array. Standing and traveling vibration modes can be separately stimulated in the container when the four-transducer array is excited with a specific signal sequence. The modal simulation is first conducted to determine the dimensional parameters and required vibration modes. Furthermore, the acoustic streaming field simulation is used to verify the effectiveness of the modal simulation and interpret the manipulation mechanism. Then, the correctness of the simulation results is demonstrated through the experiments. In the experiments, the influences of the driving frequency, target diameter, and excitation voltage on the linear manipulation are investigated through an image recognition program, respectively. The target can be linearly manipulated, and has a maximum speed of 19.10 mm s⁻¹ at 21.5 kHz. Furthermore, with the increase of the target diameter and excitation voltage, the speed of the target increases. Finally, the rotational manipulation of the targets are conducted, and the target can effectively rotate in the container at the driving frequency of 24.6 kHz. The proposed acoustofluidic manipulation device holds the merits of simple structure, low-frequency, multi-mode, and large particle manipulation ability, which may provide technical support for the detection and filter of ICF targets.

A novel piezoelectric energy harvester (z-PEH) to harness a significant amount of waste energy from human walking is proposed in the present work. The unique feature of the z-PEH is that a greater number of piezoelectric discs are planted in the z-direction without consuming a wide area of the pavement or road surface, hence termed z-PEH. This enables minimum damage to the existing pavements or roads during installation, maintenance and repair works. The power generating piezoelectric bimorphs are glued to aluminum plates attached to the hollow steel structure which is mounted on a spring. The z-PEH module consists of eight commercially available bimorphs, with each bimorph having two circular piezoelectric discs of diameter 25 mm and a thickness of 0.25 mm. The experimental and numerical open-circuit voltages of a single PZT are 9.38, 15.86 and 29.5 V and 9.23, 18.31 and 28.6 V respectively for applied weights of 24.5, 49 and 73.5 N. The z-PEH module occupied an area of 21.1 × 18 cm². The numerical design is further carried out in commercially available software ANSYS^TM with the objective of enhancing output power of the z-PEH module with in the same area. It is found out that, the optimized z-PEH module with square bimorphs, generated an open-circuit Peak-to-peak voltage of 69.07 V and the maximum DC power generated is 0.56 mW for an applied force of 73.5 N. Also, the z-PEH module with 56 bimorphs resulted in an average DC power of 3.95 mW for a step loading of 490 N (equal to 50 kg) under maximum power transfer conditions. The power density in this case is 2.49 W m⁻³.

The conductivity and dielectric properties are integral to the function of polyvinyl chloride (PVC) gel actuators. The frequency-dependent properties of PVC gel actuators are investigated here in terms of their impedance, permittivity, and for the first time, electric modulus. The data shows that PVC gels' conductive properties are just as, if not more, important as their dielectric properties in electromechanical transduction applications. The electrode polarization (EP) and its impact on the impedance and dielectric spectra of PVC gels, as well as the developed asymmetric space charge at the anode, are discussed. The electric modulus and tan $\delta$ spectra are used for the fitting of Cole-Cole (CC) and Debye relaxation models for gels of varying plasticizer content. The electrostatic adhesive force for PVC gels of varying plasticizer is also measured, indicating large electrostatic adhesion (>2 N cm⁻²). A cyclic linear voltage sweep is used to clarify the dynamics of space charge within the gels. The peak current (associated with space charge development) is seen to be concurrent with the onset of mechanical deformation, showing the asymmetric charge as the origin of electromechanical transduction. Additionally, the maximum charge transferred (as measured by the integration of current over time) before space charge development is found to correlate with the electrostatic adhesive force measured for the gels, pointing to a new method of characterizing PVC gels for actuation.

Magnetorheological elastomers (MREs) are widely used in vibration control due to their excellent magneto-controlled mechanical properties. In this research, polyurethane-based MRE polishing pads were prepared and used for the polishing of single-crystal SiC to investigate the magneto-controlled mechanical properties, the magneto-polishing effect, and the mechanism of action thereof. The results show that the pre-structuring process is affected by parameters such as mass fraction and particle size of magnetic particles in MREs and curing magnetic field strength, different chain strings that demonstrate different magnetorheological effects are formed. The greater the mass fraction of magnetic particles and curing magnetic field strength, the more the MREs exhibit magnetorheological effects, especially so when the magnetic particles size of 3 μm. A series of 90 min polishing experiments on single-crystal SiC with original surface roughness (R_a) 80 nm were conducted using an MRE pad. The results indicate that with the increase of polishing magnetic field strengths, the shear modulus of MRE polishing pads increases, the material removal rate (MRR) of the polishing process increases and R_a decreases. As the magnetic field strength is increased from 0 mT to 335 mT, the shear modulus is increased from 1.392 MPa to 1.825 MPa (an increase of 31.1%), while MRR is increased from 706.3 nm h⁻¹ to 835.3 nm h⁻¹ (an increase of 18.3%), R_a is decreased from 19.92 nm to 3.62 nm (an improvement in surface quality of 81.8%). The results show that the increase of the polishing magnetic field strengths changes the material modulus of the MRE polishing pads, which cause the decreases in the compressive and shear elastic deformation of the abrasive grains on the elastic substrate. This increases the positive pressure of the abrasive grains on the SiC wafer, which enhances the material-removal ability of the SiC wafer, thereby improving the surface quality of the wafer.

The shear thickening area formed by impact load and the restriction boundary conditions play an important role in the impact resistance and energy absorption characteristics of the shear thickening fluid (STF). In order to reveal the low speed impact resistance of STF under finite space constraints, this paper carried out research through the preparation of STF, viscosity test and design of low speed drop weight impact experiment. Firstly, STF samples with different mass fractions were prepared by self-made. Then, the rheological tests were implemented to obtain the characteristics of STF viscosity under different shear rate loads. Next, a straightforward test through rapidly pulling the glass rod out of the STF was adopted to observe the shear thickening mechanism of STF. After that, two kinds of STF samples with different mass fractions and good shear thickening performance were selected for low speed drop weight test. In the drop weight test, three containers with different geometries were designed to equivalent the finite space constraints to reveal the low speed impact resistance of STF under finite space constraints. Finally, combined with the experimental results, a series of numerical models are established to study the influence of geometric parameters in finite space on the impact resistance of STF. Through the research of this paper, the influence of geometry constraint in finite space on impact resistance of STF was obtained, which can provide reference for the geometric design of protective structure filled with STF.

Reducing the rotor dynamic load is an important issue to improve the performance and reliability of a helicopter. The control mechanism of the actively controlled flap (ACF) on the rotor dynamic load is numerically and experimentally investigated by a 3-blade helicopter rotor in this paper. In the aero-elastic numerical approach, the complex motion of the rotor such as the stretching, bending, torsion and pitching of the blade including the deflection of the ACF are all taken into consideration in the structural formulation. The aerodynamic solution adopted the vortex lattice method combined with the free wake model, in which the influence of ACF on the free wake and the aerodynamic load on the blade is taken into account as well. While the experimental method of measuring hub loads and acoustic was accomplished by a rotor rig in a wind tunnel. The result shows that the 3/rev ACF actuation can reduce the 3ω hub load by more than 50% at maximum, which is significantly better than the 4/rev control. While 4/rev has greater potential to reduce blade vortex interaction (BVI) loads than 3/rev with µ = 0.15. Further mechanistic analysis shows that by changing the phase difference between the dynamic load on the flap and the rest of the blade, the peak load on the whole blade can be improved, thus achieving effective control of the hub dynamic load, the flap reaches the minimum angle of attack at 90^∘–100^∘ azimuth under best control condition; when the BVI load is perfectly controlled, the flap reaches the minimum angle of attack at 140^∘ azimuth, and by changing the circulation of the wake, the intensity of BVI in the advancing side is improved. Moreover, an interesting finding in the optimal control of noise and vibration is that an overlap point exists on the motion patterns of the flap with different frequencies.

This study investigates the response of a shape memory alloy (SMA)-based isolation system that combines multiple groups of SMA cables and a lead rubber bearing (LRB). The isolation device, named as multi-level SMA/lead rubber bearing (ML-SLRB), is designed such that it maintains its efficiency under frequent, design and extreme levels of seismic events. Two large-size ML-SLRB isolation devices were designed and fabricated. The response of the proposed isolation systems was evaluated together with a conventional LRB under increasing amplitudes of cyclic loads. The effects of loading rate and vertical pressure on the response of the ML-SLRB isolator were evaluated. Finite element models of the fabricated ML-SLRB isolators were developed and analyzed to assess the response of the different SMA cable groups at different stages of the loading. The test results, supported by the finite element analyses, revealed that the SMA cable groups used in a loop configuration in the ML-SLRB isolator are prone to stress concentrations and early damage. The ML-SLRB isolators that employed its main SMA cable groups in a straight configuration successfully achieved a multi-level performance where the stiffness of the isolator increased as the demands of the displacement increased. The developed isolator also exhibited lower residual drifts compared to the LRB isolator.

Three most common methods for preparing PEDOT (poly(3,4-ethylenedioxythiophene)) are studied, including vapor phase polymerization (VPP), in-situ dipping (ISD) and solution deposition (SD) techniques. The PEDOT coated nonwoven fabric (PEDOT@NWF) composites were successfully fabricated via these three processes and have been proven to be conductive and equipped with piezoresistive properties. For each preparation method, factors that may affect product properties, such as concentrations of reagents, reaction temperature, reaction time, etc were explored to summarize the optimal parameters. The PEDOT@NWF composites prepared via different fabrication techniques were analyzed and compared through a series of tests and characterizations. The sensing performance of as-prepared pressure sensors are also been studied. The experimental results demonstrate that PEDOT@NWF prepared by VPP method (PEDOT@NWF-VPP) has the fastest response time (80 ms) and recovery time (40 ms), the composite prepared by ISD method (PEDOT@NWF-ISD) has the highest sensitivity for the pressure range less than 5 kPa (21.162 kPa⁻¹) and long-term cycle stability (over 5000 cycles). Sensor utilized PEDOT@NWF-ISD as the piezoresistive layer was assembled and used to detect small pressure such as voice vibrations and air flow, implying that this designed pressure sensor has promising potential in the application of wearable electronic devices and healthcare monitors.

We propose a displacement-maintaining piezoelectric actuator based on a hysteresis loop and a displacement-voltage loop. Remnant polarization and remnant strain of piezoelectric material depend on maximum applied electric field. By adjusting the peak and valley of the applied voltage, the displacement-voltage loop of piezoelectric material is changed, and our proposed actuator can have different displacement states at zero voltage. In order to verify that this actuator is practical, a commercially available piezoelectric stack using modified lead zirconate-lead titanate is used as a drive unit. Experiments show that the actuator can maintain displacement without friction. Moreover, the relationships between maintainable displacement and the peak and valley of applied voltage are obtained. The actuator can continuously adjust the maintainable displacement with nanometer-level resolution and micron-level stroke. This work provides a method to maintain continuously adjusting displacement at zero voltage without friction, which can be expected to expand the range of application of piezoelectric materials in precision actuators.

The traveling waves of linear traveling wave type piezoelectric motors are not easy to stabilize due to its finite boundary structure. The traditional two-mode excitation method is a method which can excite two modes to generate traveling waves in a finite structure. However, the drawback of the traditional method is that it does not allow for adjustment of the final output velocity. Also, this method is characterized by having low efficiency. The velocity of the generated traveling waves is constant unless the excited modes are changed. In this paper, we propose a novel method, called a two-frequency two-mode excitation method which uses a piezoelectric actuator to simultaneously excite two modes to generate traveling waves. The two frequencies chosen possess a ratio where the excited frequencies are close to two resonant modes. In addition, the two excited frequencies are simultaneously an integer ratio to a specific frequency and have a least one common multiple, as small as possible. This approach can generate stable traveling waves such that the velocity of the traveling waves can be adjusted by the two frequencies. Our theoretical predictions were validated by numerical calculations and experimental data. A Hilbert transform was used to optimize the traveling waves generated. A morphological opening was used to track the traveling wave trajectories. The obtained results show that this method can generate stable traveling waves where the wave velocity can be adjusted by mixing the frequency signals.

The concept of nanogenerators (NGs) based on textiles was introduced to impart functional attributes to textiles for developing smart textiles and integrating wearable electronics of various functionalities. The human body can generate sufficient mechanical energy that can be harvested by the piezoelectric NGs (PENGs) and used to power up low power consuming wearable electronics. Two simple and easy approaches for coating a highly conductive weave-able metal electrode with polyvinylidene fluoride (PVDF) piezoelectric polymer to construct two different types of coaxial yarn-based PENGs (Y-PENGs) are presented in this paper. The proposed techniques result in the in-situ formation of the β phase of the PVDF. The Y-PENGs are based on facile solution coating and touchspun nanofibers (TSNFs) coating of the inner electrode. The solution-coated Y-PENG (SC-YPENG) showed 5.12 V of peak open-circuit voltage (V_oc) and 41.25 nA of peak short circuit current (I_sc). Whereas the TSNFs coated Y-PENG (NFC-YPENG) showed 5.08 V of peak V_oc and 29.1 nA of peak I_sc. In a series connection, the average peak V_oc were synergized by ∼2.53 and ∼2.4 factor respectively for the SC-YPENG and the NFC-YPENG. The Y-PENGs were able to charge capacitors and run LEDs. Additionally, our coated inner electrode shows great flexibility, thereby it could be knitted or woven into smart textiles to run wearable electronics sustainably.

Carbon-based electromechanical actuators, capable of reversible shape changes in response to electrical stimuli, have found many potential utilizations such as robotic artificial muscles, micro-pumps, and sensitive switches. In this work, electroactive materials based on the dibutyl phathalate (DBP) plasticized poly(lactic acid) (PLA) and fullerene (C₆₀) were produced by a simple solvent casting method. The PLA composites exhibited fast and reversible responses under electrical stimulus. The highest storage modulus response was obtained from the 1.0%v/v C₆₀/PLA/DBP at 23.51 × 10⁵ Pa under the 1.5 kV mm⁻¹ electric field. In the bending experiment, the PLA composites bended towards the anode from the attractive force between the negative charges of the induced dipole moments namely the carbonyl groups in PLA and DBP and the π-conjugated electrons of C₆₀ and the positive electrode. The C₆₀/PLA/DBP composite with a small C₆₀ content (0.1%v/v) yielded the maximum bending distance of about 6.0 mm within 10 s and the highest dielectrophoresis force of 1.01 mN at 550 V mm⁻¹. Thus, the electrically responsive PLA composites fabricated here with the short response time and high bending deformation are demonstrated here to be promising biobased materials towards actuator applications.

The traditional monitoring methods can only give warnings for the bolts with severe looseness. However, it is essential for the safety of bolted joints to detect the looseness of bolts at the very early stage. To this end, in this paper, coda wave interferometry (CWI)-based high-resolution bolt preload monitoring using a single piezoceramic transducer is proposed. According to the CWI and acoustoelastic theories, a theoretical model is established and the linear relationship between the time shifts of coda waves and the preload variations of the bolt is derived. An experiment, in which a piezoceramic transducer simultaneously functions as the actuator and sensor, was carried out to verify the effectiveness of the proposed method. Three lead zirconium titanate transducers at different locations of a bolted specimen are tested. The experimental results show that the time shifts of coda waves increase linearly with the decrease of bolt preload and the detectable resolution of bolt preload (DRBP) is up to 0.326%. The DRBP value proves that the proposed technique can successfully monitor bolt looseness at the very early stage. In addition, a comparison study is carried out between the CWI-based method and the energy-based wavelet packet decomposition (WPD) method, and the result shows that the preload sensitivity of the CWI-based method is about six times higher than that of the WPD approach. Therefore, the CWI-based method is an effective way for the in situ monitoring of bolt looseness, especially in the embryonic stage.

In this work a novel thin-film device combining piezoelectric and contact electrification energy harvesting is created with the aim of investigating how it responds to water droplet impact during vibrations. The two energy harvesting principles utilize the same ground electrode, but the electrical signal outputs are independent and show entirely different electrical signal characteristics in presence of external forcing. While piezoelectricity gives rise to a nearly quadratic increase in harvested energy as a function of vibration velocity, the energy due to contact electrification reaches saturation for larger water drop velocities. On the other hand, when the water stream transitions from discrete droplets to a continuous stream the energy gathered from the piezoelectric mechanism exhibits saturation, whereas the energy due to contact electrification decreases. The proposed device may have applications as a self-powered environmental sensor that allow one to distinguish between forced oscillations and water droplet impacts.

Conductive composites-coated fabric sensors are favorable sensing elements for wearable applications. However, rheology of composites ingredients has been causing inaccuracy due to high hysteresis and low instantaneity in real-time measurements. To address this problem, a composites-coated fabric-based strain sensor was fabricated and studied. A physical pretreatment scheme was designed to produce cracked surface morphology on the conductive composites film, yielding a stable conductive network. Results showed that this scheme can significantly lower the electrical hysteresis of the sensors by about 35% and effectively reduce electrical and mechanical relaxation, hence notably improved electromechanical resilience of the sensors. It is also found that the linear strain-resistance property of the sensors was largely retained after pretreatment. Sensing mechanism of the cracked sensors was further derived to understand the results. Through all the observations and application prospect demonstrated by two sensing belts, it is suggested that cracking can be considered to improve sensing performance for other coated fabric flexible sensors.

Acoustic black holes (ABHs) are structural features that can be embedded into plates to provide effective structural damping. However, the performance of an embedded ABH is limited by its size, which determines the ABH cut-on frequency. It is not always practicable to increase the size of an ABH to reduce its cut-on frequency, however, previous work has shown that active vibration control can instead be used to enhance the low frequency performance of an ABH beam termination. This paper presents an investigation into the potential performance benefits that can be achieved by implementing active control into an array of ABHs embedded in a plate, realising an array of active ABHs (AABHs). The potential performance advantage is investigated here through experimental investigations, where different configurations of passive and active control treatments are applied to both a plate with embedded ABHs and a constant thickness plate. The smart structures utilise piezoelectric patches to realise the control actuation and employ an active feedforward multichannel vibration control strategy that aims to minimise the structural response monitored by an array of accelerometers. The performance of each plate configuration is evaluated in terms of the attenuation in the structural response and the energy, or control effort required. The presented experimental results demonstrate that, compared to the constant thickness plate configuration, the AABHs provide considerable passive damping above the ABH cut-on frequency and significantly reduce the required control effort.

Soft actuators with high safety, adaptivity, and energy-to-weight ratio have the potential to be used in developing more adaptive legged robots. In this work, we incorporate soft actuators into rigid parallel mechanisms and develop multi-degree-of-freedom (multi-DOF) soft-rigid hybrid joints that can actively achieve 1, 2, and 3 DOFs actuated by 2, 4, and 8 bellows-type fluidic elastomer actuators (FEAs), respectively. The FEAs exhibit large axial strain (_{e max} = 176%, _{c max} = 25%), small radial expansion (_{r max} = 12%) at 70 kPa, and are light weight, and the rigid parallel mechanisms constrain motions of the joints to the desired DOFs. We characterize the proposed joints' kinematic and static performances by measuring their range of motion and blocked torque upon actuation. Results show that these joints successfully achieve all desired DOFs and are of high torque to weight ratio (4.07 N·m·kg⁻¹). A bucking prediction model is established to evaluate the critical buckling pressure. As a demonstration for legged robots, we use the proposed joints and develop two types of multi-DOF legs based on inspirations from the DOF configuration of legged mammals' musculoskeletal systems. Preliminary results demonstrate that FEAs-based multi-DOF legs can perform fundamental biomimetic movements (e.g. leg swing) through pressure adjustment, and high-speed tasks (e.g. ball kicking and jumping) through high-pressure and short-pulse actuation.

Here, a series of thermoplastic shape memory poly(aryl ether ketone)s (PAEKs) with programmable transition temperature were synthesized via a condensation polymerization reaction. The introduction of flexible segments and side groups onto PAEK main chains promoted the formation of the alternating rigid-flexible structures and the enhanced shape memory properties. The synthesized PAEKs exhibited the great thermal stability and strength which could greatly meet the demands in engineering applications. In addition, non-contact actuation of the shape memory behaviors of PAEKs was realized through the integration of Fe₃O₄ nanoparticles with magnetocaloric effect. More significantly, small-angle X-ray scattering analysis was utilized to reveal the transition of molecular chains and phase states during the stretching and heating processes. The change of internal structures and orientation of molecular chains during the deformation process might contribute to the regulation of shape memory behaviors. These studies on the fabrication of shape memory PAEKs with non-contact magnetic actuation performances and the investigation of their structural variation during the stretching and heating process were expected to open doors for the fabrication and investigation of new type of shape memory polymers.