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Smart materials and devices that possess multiple functions of sensing and actuation have been investigated over decades as being exploited for soft robots in various applications such as artificial muscles, biomimetic actuators, and surgical tools. One of critical requirements involved is the capability of dramatic change in shape and size to be adapted for different circumstances. Recent progress of the emerging materials has showed many remarkable properties to fabricate them in simple way. This paper reports a fused deposition modeling (FDM) method that can be simply implemented by three-dimensional (3D) printing shape memory polymer (SMP) on paper. Through 3D printing of a SMP filament on paper, the bilayer structures and grippers with a starfish shape were fabricated by exploiting the cost-effective and lightweight materials. By virtue of electrothermal actuation (Joule heating) with an electrical power supply, they showed remarkable and reversible change in shape during 100 cycles of movements. As a result, it demonstrated the capability of control over adaptive shape and size in design and fabrication of soft robots. The FDM-based method in the study is therefore beneficial to extend the flexibility in design and fabrication, as compared to the conventional ones particularly applied for rigid grippers. In the near future, a variety of multi-layer structures and materials fabricated by FDM method and 3D printing materials could be applied for applications such as soft actuators and sensors in versatile conditions.

For a long time, the daily paper and carbon ink have been used for writing and painting. With the development of the electronic technology, they are expected to play new roles in electronic devices. Herein, combining the unique characteristics of the paper (rough surface, hydrophilicity) and carbon ink (conductivity), this work rationally proposed two low-cost, eco-friendly, flexible, multifunctional pressure and humidity sensors. The results show that as-fabricated paper-based (PB) pressure sensor has a good sensitivity of 0.614 kPa−1 in the pressure range of 0–6 kPa. The PB humidity sensor has a large response of ∼2120 (current ratio at 91.5% relative humidity (RH) and 0% RH). The PB pressure sensor is proven to be useful for multiple pressure related contact detections, and the PB humidity sensor can be used for many humidity related non-contact detections. Interestingly, combining the different detecting modes of pressure and humidity sensors, some same detecting functions (e.g. switch, respiratory frequency and speech recognition) are realized from contact to non-contact using PB pressure and humidity sensors, which greatly enhance the wearable comfort. Compared with previous reports, this work demonstrates a much simpler approach without expensive raw materials, toxic reagents and high temperature treatment to achieve outstanding sensing performances of the multifunctional pressure and humidity sensors.

In this study, an efficient fabrication method to realize a reversible thermo-responsive composite (TRC) and the effect of raster angle were investigated. For the facile fabrication of reversible TRCs, polylactic acid and commercial printing paper were used to generate a polymer/paper bilayer. Using the fused deposition modeling method of three-dimensional printing, three types of TRCs were fabricated and compared depending on the printing angle condition. Above the glass transition temperature, the polymer is relaxed, allowing straightening by the constraining paper layer; subsequently, it recovers its initial shape during cooling. Because the deposited filament arrays shrank in the longitudinal direction and expanded in another direction during heating, the raster angle was considered for better actuating performance. Thus, horizontal-type TRCs exhibited a greater range of average actuating performance compared with vertical-type TRCs (up to ∼24.7% increase in changing rate). Hence, this study supports a rapid, low-cost, and efficient fabrication method for soft robotics applications, including smart devices, grippers, and actuators.

Cellulose-based electro-active paper (EAPap) has been reported as a smart material that has merits in terms of light weight, dry condition, biodegradability, large displacement output and low actuation voltage. However, it requires high humidity. This paper introduces an EAPap that can be actuated in low humidity conditions. The fabrication process and performance test of the EAPap actuator are illustrated. Cellulose fibers were dissolved in N,N-dimethylacetamide/lithium chloride. The solution was cast and immersed in water to form the cellulose film, followed by adding glycerol and lithium chloride aqueous solution, and drying in air. Depositing thin gold electrodes on both sides of the cellulose film made a bending EAPap actuator. Effects and optimum values of the glycerol content and the thickness of the films are discussed.

A micro-patterning technique regarded as micro transfer printing is studied for gold electrode patterning on cellulose electro-active paper (EAPap), aiming at biodegradable and flexible MEMS fabrication. EAPap is known as a smart material due to the interesting actuation phenomenon of cellulose paper. Accordingly, EAPap can be used for sensor and actuator devices. Since EAPap is made with cellulose, a biodegradable and flexible MEMS device can be made with this material. However, since cellulose-based EAPap is hydrophilic and flexible, conventional lithography and etching techniques cannot be used for micro-patterning. This paper reports a new micro-patterning technique using the micro transfer printing (MTP) method on flexible EAPap material. The MTP technique consists of a master fabrication, a polydimethylsiloxane (PDMS) stamp construction, and a micro pattern transfer. Details of the technique and key issues are addressed. To demonstrate the feasibility of the MTP technique, a gold electrode pattern for a surface acoustic wave (SAW) MEMS device and a gold micro-strip pattern for a microwave dipole rectenna are made on cellulose paper substrates.

Electro-active paper (EAPap) is attractive as an electro-active polymer (EAP) actuator material due to its low weight, dry condition, large displacement output, low actuation voltage and low power consumption and biodegradability. EAPap is made from cellulose. Cellulose fibre is dissolved into a solution and made into a sheet, then thin electrodes are deposited on the cellulose paper to make an EAPap actuator. The performance of EAPap actuators was evaluated in terms of tip displacement, blocking force and electrical power consumption. The maximum tip displacement of 4.3?mm was obtained from a 40?mm long EAPap actuator when 0.25?kV?mm?1 was applied. This actuation voltage is quite low compared with other electronic EAP materials. The effect of the environment in terms of humidity and temperature was also investigated. When the relative humidity was increased up to 95%, the tip displacement increased. When the temperature was increased the displacement slowly increased and then gradually decreased after the temperature reached 30??C. These measurements were performed under a variety of environmental and input factors including frequency, actuation voltage, temperature and humidity.

Actuators based on cellulose paper with conducting polymer (CP-EAPap) as an electrode material were constructed. The bilayer and trilayer types of actuators were fabricated by depositing conducting polypyrrole on one side and two sides of cellophane paper respectively, which was previously gold coated. By varying the deposition time, the electrode thickness was manipulated. The performance of these two types of actuators was compared with respect to humidity changes and thickness variation. The electrode thickness plays a key role in the displacement behavior of these types of actuators. The best performance at higher humidity is also characteristic of CP-EAPap actuators. The possible mechanism of actuation is addressed in this paper.

Multi-walled carbon nanotube (MWNT)-mixed cellulose electro-active paper (EAPap) was fabricated and its bending actuation performance and characteristics were tested. Cellulose fibers were dissolved using DMAc solvent and MWNT were mixed by using sonication. The very fine surface of DMAc cellulose film was fabricated using an in situ pressurized hydrolysis process. By mixing a small amount (0.1 wt%) of MWNT in the DMAc cellulose, enhancement of the MWNT-mixed cellulose EAPap actuator was demonstrated in terms of Young's modulus, resonance frequency and mechanical power output. The actuation principle of the actuator is also discussed.

Cellulose based electro-active paper (EAPap) has been discovered as an attractive EAP material for artificial muscles due to its advantages in terms of light weight, biodegradability, low cost, large displacement output, low actuation voltage and low power consumption. However, EAPap exhibits low force output and frequency band. To enhance EAPap actuators, a hybrid EAPap actuator is developed by coating a composite of single-walled carbon nanotube (SWNT)/polyaniline (PANi) with different dopants (Cl− and ClO4−). SWNT is dispersed in 1-methyl-2-pyrrolidone (NMP), and the SWNT suspension is mixed and sonicated with dopants. The resulting solution is coated on both sides of EAPap by spin coating. The actuation performance of hybrid EAPap actuators is tested in terms of bending displacement, blocked force, mechanical power output and electrical power consumption. The hybrid EAPap actuators show improved force and resonance frequency as a result of enhanced stiffness of the actuators. Although the displacement output is a little bit decreased, the required electrical field strength and the electrical power consumption are low, which are promising for achieving ultra-lightweight smart actuators.

In this paper, the actuation mechanism of electro-active paper (EAPap) actuators is addressed and the potential of the actuators is demonstrated. EAPap is a paper that produces large displacement with small force under an electrical excitation. EAPap is made with a chemically treated paper by constructing thin electrodes on both sides of the paper. When electrical voltage is applied on the electrodes the EAPap produces bending displacement. However, the displacement output has been unstable and degraded with timescale. To improve the bending performance of EAPap, different paper fibers - softwood, hardwood, bacteria cellulose, cellophane, carbon mixture paper, electrolyte containing paper and Korean traditional paper, in conjunction with additive chemicals, were tested. Two attempts were made to construct the electrodes: the direct use of aluminum foil and the gold sputtering technique. It was found that a cellophane paper exhibits a remarkable bending performance. When 2 MV m-1 excitation voltage was applied to the paper actuator, more than 3 mm tip displacement was observed from the 30 mm long paper beam. This is quite a low excitation voltage compared with that of other EAPs. Details of the experiments and results are addressed.

Electrically aligned regenerated cellulose films were fabricated and the effect of applied electric field was investigated for the piezoelectricity of electro-active paper (EAPap). The EAPap was fabricated by coating gold electrodes on both sides of regenerated cellulose film. The cellulose film was prepared by dissolving cotton pulp in LiCl/N,N-dimethylacetamide solution followed by a cellulose chain regeneration process. During the regeneration process an external electric field was applied in the direction of mechanical stretching. Alignment of cellulose fiber chains was investigated as a function of applied electric field. The material characteristics of the cellulose films were analyzed by using an x-ray diffractometer, a field emission scanning electron microscope and a high voltage electron microscope. The application of external electric fields was found to induce formation of nanofibers in the cellulose, resulting in an increase in the crystallinity index (CI) values. It was also found that samples with higher CI values showed higher in-plane piezoelectric constant, d31, values. The piezoelectricity of the current EAPap films was measured to be equivalent or better than that of ordinary PVDF films. Therefore, an external electric field applied to a cellulose film along with a mechanical stretching during the regeneration process can enhance the piezoelectricity.

The possibility of cellulose-based electro-active paper (EAPap) as a vibrational energy transducer was investigated in this paper. Thin cellulose EAPap film specimens were prepared by the regenerating process. Three different metal electrodes of gold, silver and aluminum were deposited on a 50 ? 50?mm2 cellulose film using a thermal evaporator. An aluminum cantilever beam was used as a vibrational bender and EAPap was attached close to the root of the cantilever beam. The voltage output of the EAPap was measured under harmonic base excitation of the cantilever beam. The EAPap with aluminum electrode provided the largest open circuit voltage output compared to those with gold or silver electrodes. The output voltages of the EAPap increased linearly with increase of the area of the electrodes. The output voltages also increased with increasing input acceleration but became saturated at a certain magnitude. From the experimental results, we conclude that EAPap with metal electrodes can be used as a flexible energy harvesting transducer by external mechanical stress, and the output voltage is related to the electrode material due to its work function.

The 5th World Congress on Biomimetics, Artificial Muscles and Nano-Bio and the 4th International Conference on Artificial Muscles were held in Osaka, Japan, 23–27 November 2009. This special section of Smart Materials and Structures is devoted to a selected number of research papers presented at this international conference and congress. Of the 76 or so papers presented at the conference, only 10 papers were finally selected, reviewed and accepted for this special section, following the regular reviewing procedures of the journal. This special section is focused on polymeric artificial muscles, electroactive polymers, multifunctional nanocomposites and their applications. In particular, an electromechanical model for self-sensing ionic polymer–metal composite actuating devices with patterned surface electrodes is presented which discusses the concept of creating self-sensing ionic polymer–metal composite (IPMC) actuating devices with patterned surface electrodes where actuator and sensor elements are separated by a grounded shielding electrode. Eventually, an electromechanical model of the device is also proposed and validated. Following that, there is broad coverage of polytetrahydrofurane–polyethylene oxide–PEDOT conducting interpenetrating polymer networks (IPNs) for high speed actuators. The conducting polymer (poly(3,4-ethylenedioxythiophene)) is incorporated within the IPNs, which are synthesized from polyethylene oxide (PEO)/polytetrahydrofurane (PTHF) networks. PEO/PTHF IPNs are prepared using poly(ethylene glycol) methacrylate and dimethacrylate and hydroxythelechelic PTHF as starting materials. The conducting IPN actuators are prepared by oxidative polymerization of 3,4-ethylenedioxithiophene (EDOT) using FeCl3 as an oxidizing agent within the PEO/PTHF IPN host matrix. Subsequently, giant and reversible magnetorheology of carrageenan/iron oxide magnetic gels are discussed and the effect of magnetic fields on the viscoelastic properties, magnetorheological effect of carrageenan gel containing iron oxide particles are investigated using dynamic viscoelastic measurements under magnetic fields. Furthermore, the relationship between the magnetorheology and the elasticity of magnetic gel is discussed. This special section then covers the characteristics of ionic polymer–metal composite with chemically-doped TiO2 particles to improve the bending performance of ionic polymer–metal composite (IPMC) actuators. This study is mainly focused on the characterization of the physical, electrochemical, and electromechanical properties of TiO2-doped ionic polymer membranes, and IPMCs prepared by the sol–gel method, which results in a uniform distribution of the particles inside the polymer membrane. It was determined that the lifetime of IPMC is strongly dependent on the level of water uptake. This paper is then followed by a presentation on training and shape retention in conducting polymer artificial muscles. Electrochemomechanical deformation (ECMD) of the conducting polymer, polyaniline film, is studied to investigate the behavior of actuation under tensile loads. The ECMD is induced by strains due to insertion of ionic species (cyclic strain) and a creep due to applied loads during the redox cycle. The cyclic strain is enhanced by the experience of high tensile loads, indicating a training effect. The training effect is explained by the enhanced electrochemical activity of the film. The special section then presents a paper on the current status and future prospects of power generators using dielectric elastomers. Electroactive polymer artificial muscle (EPAM), known as 'dielectric elastomer', appears to offer unique capabilities as an actuator and electrical power generator. However, the power output levels of such generators are small and the efficiencies are rather high. For example, electrical energy conversion efficiency of over 70% has been achieved. The ability of EPAM to produce hydrogen fuel for energy storage was also demonstrated. Because the energy conversion principle of EPAM is capacitive in nature, the performance is largely size-independent. Formation of motile assembly of microtubules driven by kinesins is presented next. Microtubule (MT) and kinesin are rail and motor proteins that are involved in various moving events of eukaryotic cells in natural systems. In vitro, the sliding motion of microtubules (rail) can be reproduced on a kinesin (motor protein)-coated surface coupled with adenosine triphosphate (ATP) hydrolysis, which is called a 'motility assay'. Based on this technique, a method is reported for forming MT assemblies by an active self-assembly (AcSA) process, in which MTs are crosslinked during a sliding motion on a kinesin-coated surface. Streptavidin (ST) is employed as glue to crosslink biotin-labeled MTs. This discussion is then followed by a paper on the performances of fast-moving low-voltage electromechanical actuators based on single-walled carbon nanotubes and ionic liquids. Here the mechanical and electrical properties of the polymer-free single-walled carbon nanotube (SWNT) sheets containing different contents of ionic liquids (ILs) are reported. The polymer-free SWNT sheets are prepared with the knowledge that millimeter-long 'super growth' carbon nanotubes (SG-SWNTs), produced by a water-assisted modified CVD method, associate together tightly with ILs. The molecular mechanism of electroactive polymer actuators is then discussed in the next paper. Movement of ionic electroactive polymer actuators utilizes their anisotropic volume change, which is induced by the applied voltage. The mechanism of the volume change is, however, not well understood, especially at the molecular level. The current understanding of the mechanism of the volume change at the molecular level is reviewed, focusing on the actuators made with carbon materials. Then, the pressure generated in the actuators in response to the applied voltage based on the results of the Monte Carlo simulation is discussed. It is shown that the mechanism of the actuators can be analyzed at the molecular level in terms of the balance between the electrostatic and volume exclusion interactions that act among the electrode materials and the electrolyte ions. The special section then presents a master curve for analyzing the electrochemical aging and memory effects of poly(3,4-ethylenedioxythiophene). The memory effect of conducting polymers in an electrochemical environment is investigated. This memory effect is related to the electromechanical responses of the conducting polymer. Poly(3,4-ethylenedioxythiophene) is chosen because of its interesting properties—mainly its chemical and electrochemical stabilities. By means of cyclic voltammetry, the influence of the waiting time tw at a holding potential Ew in relation to the conformational relaxation process occurring in the conducting polymer is analyzed. The effect of electrochemical aging on the electrical properties is also explained from the viewpoint of the rearrangement of polymer chains. This completes a brief report on the content of the special section on artificial muscles. I would like to thank the contributing authors of this collection of papers on artificial muscles for their outstanding and unique contributions. I am also indebted to all of the reviewers, editors and editorial staff who handled the reviews of all the papers for their time and effort. I would like to express my sincere thanks and appreciation to Professor E Garcia, Editor-in-Chief, for his encouragement and support, and for providing the opportunity to publish this special section of Smart Materials and Structures. I am also grateful to the IOP Publishing team for their support. In particular, I am greatly indebted to publisher Natasha Leeper, for her help and excellent management in the preparation of this special section on artificial muscles.

The 20th International Conference on Adaptive Structures and Technologies (ICAST) was held on 20–22 October 2009 in Hong Kong. This special section of Smart Materials and Structures is derived from the research papers presented at the conference. Of the 106 papers presented at the conference, 11 papers were reviewed and accepted for this special section, following the regular review procedures of the journal. This special section is focused on smart materials, multifunctional composites, and applications on morphing structures. Smart materials. Smart materials are the foundation of adaptive structures and intelligent systems. The development of new materials will lead to significant improvement in various applications. Three articles are focused on the fabrication of new materials and investigation of their behaviors: Barium strontium zirconate titanate ((Ba1-xSrx)(ZrxTi1-x)O3; BSZT, x = 0.25 and 0.75) ceramics with a highly crystalline structure were fabricated using the combustion technique. The microstructure of BSZT powders exhibited an almost-spherical morphology and had a porous agglomerated form. Polyaniline (PANI)/clay nanoparticles with unique core-shell structure were synthesized via Pickering emulsion polymerization. By dispersing PANI/clay nanoparticles in silicone oil, the ER fluid was made. Magnetic field effects were investigated on the deposition rate and surface morphology of chromium nitride coatings deposited by magnetron sputtering for superior hardness, excellent wear and oxidation resistance. The surface morphology of chromium nitride films was also examined by a scanning electron microscope (SEM). Multifunctional composites. Composites are made from two or more constituent materials so they can combine the best properties of different materials. Five papers deal with fabrication, testing, and modeling of various multifunctional composites: A new active structural fiber (ASF) was fabricated by coating a single carbon fiber with a concentric PZT (PbZr0.52Ti0.48O3) shell using electrolytic deposition. This new ASF is expected to have broader applications due to the higher piezoelectric coupling effect with the use of carbon fiber and PZT. The sol-gel technique was employed to deposit lead zirconium titanium (PZT) and silica composite film onto a copper (Cu)/polyimide (PI) flexible structure. The fabricated PZT-silica composite films were then used for flexible actuator and sensor applications. Interfacial properties and hydrophobicity of multifunctional Ni-nanopowder/epoxy composites were evaluated for self-sensing and actuation. The effects of water content on the actuation performance of ionic polymer–metal composites (IPMCs) were investigated experimentally. Multiscale modelling of a composite electroactive polymer structure was developed, in particular for tubular actuators. The models were validated with experimental data. Morphing structures. Three papers relate to morphing skins and structures. Several issues including stiffness and energy consumption were explored: Composite corrugated structures were used as morphing skin panels (MSPs) in the trailing edge region of a scaled morphing aerofoil section. Wind tunnel testing was carried out to demonstrate the MSP concept. Optimization of a variable-stiffness skin was performed for morphing high-lift devices. The objective is to design the structure to have high enough stiffness to withstand aerodynamic loading and yet low enough stiffness to enable morphing. The aerodynamic and actuation loads were taken into consideration during the optimization. Two adaptive and morphing structures were proposed for low-energy consumption or even energy-harvesting green buildings with the use of an optimization process. Searching for optimal solutions was done by means of an evolutionary technique while the compatibility of the resulting configurations of the adaptive envelope was ensured by the virtual force density method. We would like to thank all of the authors for their significant contributions to this special section for Smart Materials and Structures. We are also grateful to all of the reviewers and associate editors who handled the reviews for their time and effort. I would like to express my sincere appreciation to Professor E Garcia, Editor-in-Chief, for his encouragement by providing the opportunity to make this special section. I am indebted to IOP Publishing for their strong support and the staff, in particular publisher Natasha Leeper, for their special attention and excellent service.

This paper reports a wirelessly driven electro-active paper actuator that consists of a dipole rectenna array, a power control circuit and two cellulose–polypyrrole–ionic liquid (CPIL) electro-active paper actuators. The CPIL nanocomposite actuator was fabricated by incorporating nanoscaled PPy onto cellulose by an in situ polymerization technique, which was followed by activation in a room temperature ionic liquid. The CPIL actuator shows its maximum bending displacement of 10 mm at an ambient humidity condition with 30 mW electrical power consumption. The CPIL actuator is very stable in its actuator performance. The dipole rectenna array receives microwaves and converts them to dc power so as to wirelessly supply power to the actuators. Three flexible dipole rectenna arrays are designed, manufactured and characterized. The rectenna array that has nine rectenna elements generates the maximum power of 75 mW. This power was used to successfully activate the two CPIL actuators and the control circuit. Detailed fabrication and characterization of the CPIL actuator and the dipole rectenna array as well as the control circuit are explained.

This paper reports a cellulose–polypyrrole–ionic liquid (CPIL) nanocomposite that can produce large actuating displacement in a low humidity environment. The fabrication process and actuator performance of the CPIL nanocomposite actuator are illustrated. Experimental results revealed that the size of anion, concentration of ionic liquid and ambient humidity level have a significant influence on the actuator performance of the CPIL nanocomposite. The bending displacement of the CPIL nanocomposite actuator was enhanced with increasing anion size, ionic liquid concentration and humidity level. CPIL nanocomposite made with 4% BMIBF4 ionic liquid exhibited a very large bending displacement with excellent durability under ambient conditions (30% relative humidity and 25 °C). This is probably the first report that cellulose based electro-active paper actuator can exhibit such a large bending displacement under ambient conditions. Experimental results revealed that the proposed CPIL nanocomposite actuator under study can be operated up to 70% humidity level.

This paper reports polyaniline and cellulose blended electro-active paper (EAPap) that can produce large bending displacement at ambient humidity conditions with long lifetime durability. A novel solution processable polyaniline-p-toluene sulfonate (PANI–PTSA) salt was prepared by an inverted emulsion polymerization technique using benzoyl peroxide and p-toluene sulfonic acid. Cellulose solution prepared by dissolving cotton with lithium chloride/N, N-dimethylacetamide was mixed with the PANI emaraldine salt solution and a cellulose–PANI blended film was obtained. The obtained cellulose–PANI film was characterized by ultraviolet–visible (UV–visible), x-ray diffraction, scanning electron microscopy and tensile test methods. A cellulose–PANI EAPap actuator was made by depositing very thin gold electrodes on both sides of the cellulose–PANI film. When the actuator performance of the cellulose–PANI EAPap was evaluated in terms of bending displacement with respect to the actuation frequencies, voltages and relative humidity levels, a large bending displacement was shown at ambient humidity conditions with long lifetime durability.

The mechanical properties of cellulose-based electro-active paper (EAPap) are investigated under various environmental conditions. Cellulose EAPap has been discovered as a smart material that can be used as both sensor and actuator. Its advantages include low voltage operation, light weight, low power consumption, biodegradability and low cost. EAPap is made with cellulose paper coated with thin electrodes. EAPap shows a reversible and reproducible bending movement as well as longitudinal displacement under an electric field. However, EAPap is a complex anisotropic material which has not been fully characterized. This study investigates the mechanical properties of cellulose-based EAPap, including Young's modulus, yield strength, ultimate strength and creep, along with orientation directions, humidity and temperature levels. To test the materials in different humidity and temperature levels, a special material testing system was made that can control the testing environmental conditions. The initial Young's modulus of EAPap is in the range of 4–9 GPa, which was higher than that of other polymer materials. Also, the Young's modulus is orientation dependent, which may be associated with the piezoelectricity of EAPap materials. The elastic strength and stiffness gradually decreased when the humidity and temperature were increased. Creep and relaxation were observed under constant stress and strain, respectively. Through scanning electron microscopy, EAPap is shown to exhibit both layered and oriented cellulose macromolecular structures that impact both the elastic and plastic behavior.

The creep deformation process of an electro-active paper (EAPap) actuator was investigated by adapting stepwise dead-weight loading. To understand the deformation mechanism of the EAPap film, including morphological and structural changes, various loading conditions below yield strength were applied to cellophane EAPap. From the structural observation, micro-dimples and micro-cracks were detected at applied load lower than 10% of yield strength, while they were not found in higher load conditions. It is hypothesized that only short and random fibers in the amorphous region may respond to the applied stress at the low loading condition, not the fibers in the crystalline area. As a result, deformation energy at the localized spot accumulated and created micro-defects at the surface. Meanwhile, fibers in the crystalline region may sustain most of the loads as creep load increases to a high level. Molecular chains in the fiber may rotate and elongate with high load. Elongated fibers were observed only at a high level of load. From the structural change as a function of applied load, a peak shift of crystal orientation was observed only in high load conditions by wide angle x-ray measurement. This may confirm that creep deformation could give rise to structure changes in EAPap.

The mechanical stretching effect on the actuating performance of electroactive cellulose paper (EAPap) was studied. A lattice elongation of cellulose fibrils due to in-plane tensile stress along the stretching direction was observed by the x-ray diffraction method. The shrinkage of the fibril diameter as a function of stretching ratio was confirmed by surface and cross-sectional images. While the actuator performance in terms of bending displacement decreased as the stretching ratio increased, the resonance frequency linearly increased as the stretching ratio increased, which was compared with the theoretical frequency data found from a cantilever beam model. The actuator efficiency was evaluated from the electrical input power consumption and the mechanical output power of an EAPap actuator. It was revealed that the stretching process increased the electro-mechanical efficiency of the EAPap actuator. The mechanism of the influence of the stretching effect on the performance of an EAPap actuator is discussed.

We studied the effect of chitosan blending on the electrical property of chitosan-blended cellulose electroactive paper (EAPap) under different humidity conditions. As the chitosan blending ratio increased, the real part of the dielectric constant of chitosan-blended cellulose EAPap increased while the dielectric loss factor decreased. From the curve fitting of the measured data using an electrode polarization model, it was found that increasing the chitosan ratio in the EAPap might promote a decrease in the relaxation time of the EAPap, resulting in an increase of the ion mobility and dc conductivity. Over 30% of the chitosan blending ratio, a gradual increment of the ion mobility of the EAPap was observed at 40% relative humidity, while a quadratic increment of the mobility was found at 60% relative humidity condition. This kind of ion-mobility-enhanced cellulose EAPap can be used not only for bending actuators but also for medical applications such as blood clotting patches.

Cellulose-based electro-active paper (EAPap) has been reported as a smart material that has merits in terms of light weight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage. However, its actuator performance is very sensitive to humidity and degrades with time. To solve these drawbacks, we introduce an EAPap actuator made with cellulose and chitosan blend films. Cellulose?chitosan blend films were prepared by dissolving the polymers in trifluoroacetic acid as a co-solvent followed by spin-coating onto glass substrates. A bending EAPap actuator is made by depositing thin gold electrodes on both sides of the cellulose?chitosan films. Characteristics of these blend films are performed by FT-IR, XRD, TGA, SEM and a pull test. The electromechanical performance of the EAPap actuator is evaluated in terms of free bending displacement with respect to the actuation frequency, voltage, time variation and humidity levels. Results show that this chitosan?cellulose-based EAPap actuator is less sensitive to humidity: it shows a large bending displacement (about 4.1?mm) and long lifetime (more than 9?h) at room humidity conditions. It indicates that this chitosan?cellulose EAPap is promising for many biomimetic applications in the foreseeable future.

This paper presents a detailed investigation on an asymmetric magnetic-coupled bending-torsion piezoelectric energy harvester based on harmonic excitation. There is an eccentricity between the shape center of moving magnets and the axis of the piezoelectric beam, which results in the bending and torsion simultaneously in working condition. The distributed mathematical model is derived from the energy method to describe the dynamic characteristics of the harvester, and the correctness of the model is verified by experiments. To further demonstrate the improvement performance of the proposed energy harvester, the bending-torsion energy harvester (i.e. magnetic-coupled was not configured) is experimented and compared. The theoretical and experimental results indicate that the average power increases about 300% but the resonance frequency decreases approximately 2 Hz comparing to the harvester without magnetic-coupled. According to the characteristic of distributed parameter model, the magnetic force and the size of the piezoelectric beam are investigated respectively. And the lumped-parameter model is introduced to analyze the steady-state characteristic. Accordingly, this paper provides a feasible method to improve performance for piezoelectric energy harvester.

The electro-mechanical impedance (EMI) technique has emerged as a cost-effective and non-destructive technique to detect the possible damages in the structure using a piezoelectric transducer, especially, lead zirconate titanate (PZT). The adhesive bond layer plays an important role in the PZT patch-host structure interaction for monitoring structural damage. Two bonding conditions are investigated in this research paper. Primarily, the debonding phenomenon of the adhesive bond layer may misinterpret the EMI response on the damage caused in structure. Subsequently, the investigation included the protective layer at the top of the PZT transducer to avoid sensor degradation. However, the analytical models developed so far have not considered a protective layer at the top of the PZT transducer. This paper presents the novel two-dimensional (2D) analytical model for incorporating debonding concepts and the new refined 2D analytical model to include a protective layer in the study of surface-bonded PZT transducers. The proposed analytical models are verified with the experimental studies. The experimental and analytical results show good agreement, which confirms the effectiveness of the new models. This paper also incorporated the effect of each bonding condition for monitoring structural damage by implementing the EMI technique. For the simulation, the numerical investigations on the PZT transducer bonded on the metallic (aluminum and steel) and concrete blocks are performed using coupled field analysis through finite element (FE) modeling. It is found that each bonding condition has influenced the resulting signatures. The signatures obtained from developed theoretical models and numerical simulations using three-dimensional FE models for each bonding condition are compared to highlight the influence on structural damage detection. The trend of signatures is found to be matching satisfactory. Several parametric studies have been conducted to show the efficacy of the new refined model with a protective layer. It considers the different input properties of an adhesive layer, host structure, and temperature conditions. The influence of debonding of the protective layer is also studied, and the obtained results support the need for a protective layer in the models.

In the course of flight, morphing skins play an important role in morphing aircrafts. Shape memory polymer (SMP) with variable stiffness performance is a good candidate material for skin. In this paper, a series of SMP morphing skins were prepared from hydro-epoxy resin, carboxyl-terminated butadiene acrylonitrile (CTBN) and maleic anhydride. By adjusting molecular weight and content of CTBN, in-plane properties and out-of-plane properties of morphing skins can be adjusted. Due to the in-plane tensile stress acting on the skin during flight, tensile test was carried out to study its in-plane performance. After testing, skin can resist maximum in-plane tensile strength of 63.7 MPa. As for the out-of-plane performance of the skin, shape memory test was studied in this paper. All morphing skins have 100% shape fixity rate (Rf) and fast shape recovery rate (Rr). When toughened by CTBN of 10% of 4000 molecular weight with a mass fraction, the skin can recover its out-of-plane deformed shape in 33 s. The SMP skins were proved to be a promising candidate for morphing skins.

Structural health monitoring (SHM) systems have a potential to reduce lifecycle costs of structures. They may be used for maintenance planning which reduces the maintenance cost as well as for lifetime extension. As a result, there is a lot of active research in the area for SHM of civil and mechanical structures. The SHM system should be low cost, suitable for continuous monitoring, able to detect small levels of damage. Guided waves (GW) based SHM techniques allow monitoring of large plate-like structures with few sensors and have been identified as the most promising of techniques for SHM. Several different actuators and sensors have been developed and used for the GW based SHM. FBG sensors due to their low weight, and ability to be multiplexed have been long thought to be an ideal sensors for SHM. The recent development of the edge filtering approach has increased their sensitivity to GW sensing and made them ideal sensors. Unfortunately the FBG sensors are passive sensors and show directional sensitivity. These operational constraints make extension of the earlier developed GW based SHM techniques for FBG sensors difficult. Recently the authors developed a technique for damage detection specifically designed for a network with FBG sensors. This paper develops a methodology for a design of an actuator-sensor (AS) network for improving the damage assessment capability using the developed method. The paper develops a two-step methodology for the optimization of actuator placement for an AS network with FBG sensors. In the first step the number of actuators needed for the optimization are determined based on actuator densities. Once the number of actuators is known, a genetic algorithm (GA) is developed for the optimization of the their positions. The cost function is developed based on two new metrics (namely coverage2—coverage with at least 2 AS pairs and coverageR—radial coverage based on edge reflections) which are defined by the application demand. The optimized placement is then used to successfully detect and localize the damage. The study also shows the merit in the use of the specific metrics and the sufficiency of the metrics developed for improving the damage detection capability of the specific method.

This paper demonstrates the key process optimizations that need to be carried out in order to leverage the piezoelectric property of polyvinylidene diflouride (PVDF) thin films for miniaturized sensor and actuator applications. The emphasis of the paper is two fold. Firstly, innate material and piezoelectric properties of PVDF thin films were thoroughly investigated and the processing conditions for achieving minimally porous, smooth thin film exhibiting superior piezoelectric response was experimentally figured out. Along with that, as a proof of concept, a working prototype of piezoelectric micromachined ultrasonic transducer (PMUT) was fabricated and tested using optimized PVDF thin films. The key bottleneck of adhesion of PVDF with underlying metal layers is addressed by using adhesion promoter (3-aminopropyl)triethoxysilane. This small, yet significant modification enabled the fabrication of PMUT device using PVDF as membrane material. The fabricated device has exhibited a electromechanical coupling coefficient value of 15.66% and a resonance frequency of 129.5 kHz.

This paper discusses a new model and experimental characterization for thermal responses of straight twisted polymer fiber (TPF) actuators in blocked torsion. The proposed model is derived from combining the fiber stiffness matrix with Shafer’s model of free torsion. The derived model predicts that the blocking torque increases as the initial twist increases. Although it is not widely recognized, the tension of a straight TPF decreases as the initial torsion increases, and this paper explains this fact. The proposed model predicts the decrease in tension by using Shafer’s kinematic model that considers the effect of radial thermal expansion. Experimental characterization and model verification are performed using nylon 6 (polyamide 6) fiber samples with ten different initial twists, ranging from weak to strong. The results indicate that as the initial twist increases, the torque increases and the tension decreases. The tension fluctuates with respect to time. The experimental results show that the shear modulus increases as the initial twist increases. The predictions of the proposed model are reasonably consistent with the experimental thermal responses of straight TPFs in blocked torsion when the constants obtained by experimental characterization are used.

Performance tests of magnetorheological (MR) dampers show that the hysteresis curves generally show an obvious force–lag phenomenon, which is due to the presence of trapped air in the working chamber of the damper. However, the force–lag phenomenon is barely considered in existing studies, and its influence on the seismic performance of MR damped structures is still unclear. In this paper, experimental and theoretical research have been carried out to analyze the force–lag phenomenon and its influence. Firstly, a specially designed MR damper was manufactured so that MR fluid can be poured into the damper successively for several times until the working chamber was filled, and performance tests were carried out correspondingly with different MR fluid perfusion densities (a parameter introduced in this paper to describe the volume fraction of MR fluid in the working chamber). The mechanical properties of the MR damper under different MR fluid perfusion densities were compared to reveal the influence of the force–lag phenomenon. Then, the effects of excitation properties on the force–lag phenomenon were discussed by comparing experiments results under different currents, frequencies and displacement amplitudes. Further, a force–lag mathematical model was proposed by considering the variation of the force-lag part with MR fluid perfusion density to reflect the force–lag phenomenon with different volume fractions of trapped air, and then verified based on the performance test data. Finally, numerical analysis of MR damped structures with different MR fluid perfusion densities was performed using the proposed force–lag mathematical model. Results show that the damping effect of MR control systems will be weaken due to the force–lag phenomenon, and with the increase of the MR fluid perfusion density, the seismic performance of MR damped structures will gradually improve.

The research presented in this paper was aimed at developing spacer warp knitted thermoelectric generators (TEGs), which can generate electrical current from waste heat. Hence, this paper introduces a structural design approach and a calculation model in addition to describing the manufacturing of prototypes and analyses on their basic functionality regarding thermoelectric power generation. Wires as well as wire strands of iron and constantan can be used for knitting on a double bar raschel machine. Wires can be connected to a thermocouple (TC) by means of various spacer warp knitting patterns while using the feed system of the spacer yarn for the wires. The friction locking electrical contacting of several TC, thus forming an applicable TEG, was achieved by sewing together silver plated copper wire strands. A large wire cross section, clear separation of iron and con-stantan wires in the knitted fabric, and consistently high temperature difference between the TEG surfaces produce a constant thermoelectric voltage. The maximum voltage depends on the number of TC, the material properties, and the temperature difference. By reducing the internal resistance of the TEG, electric power can be increased.

The filled elastomer materials exhibit obvious stress-softening phenomenon after initial stretching, which is called the Mullins effect. Since magnetorheological elastomers tend to work under a magnetic field, it will show a different magneto-induced Mullins effect of traditional materials. Therefore, in this paper, the effects of anisotropy, magnetic flux density, pre-strain and compression times on the magneto-induced Mullins effect were studied by rheometer. The results demonstrated that, under a fixed magnetic flux density, when the arrangement of magnetic particles is perpendicular to the magnetic field, the residual strain energy of the material is the smallest. This indicates that the magneto-induced Mullins effect is the weakest and the stability of the material is the best. Meanwhile, when the compression pre-strain is constant, the materials will show an obvious stress-hardening phenomenon under magnetic field. When the arrangement of magnetic particles is 30° to the magnetic field, the force between the particles is the smallest. This indicates that the magneto-induced Mullins effect is the weakest and the performance stability is the best. At the same time, this paper attempts to establish the corresponding model of the magneto-induced Mullins effect from the perspective of strain energy. The error between the fitting and the experimental results is less than 3%, which shows that the model can well explain the phenomena obtained in the experiment.

The bridge stay cable, one of the most critical components in cable-stayed bridges, is vulnerable to vibrations owing to its low inherent damping capacity. Thus effective vibration control technology for bridge stay cables is extremely critical to safe operations of cable-stayed bridges. Several countermeasures have been presented and/or implemented to mitigate this vibration; however the passive method can only add a small amount of damping to the cables, excessive energy demand of active control devices severely limits its practicality, the semi-active control methods still have the drawbacks of complex state estimation module and a large amount of control algorithm calculation. This paper proposes a practical magnetorheological pseudo negative stiffness (MR-PNS) control system coupled with control strategy for bridge stay cables. The current reference point is introduced in the dynamic modeling of the MR-PNS control system to characterize the current control strategy. This paper investigates the adjustable of MR-PNS control system performance and energy consumption caused by different current strategies. Taking the vibration control of the Nanjing Second Yangtze River Bridge J20 cable as an example, the simulation results highlight the advantages of the MR-PNS control system that the failure area is small, the quasi-optimal area is wide, and it can still keep sort of vibration damping performance in the degenerate area. The model cable vibration control test proves the feasibility and efficiency of the single input MR-PNS bridge stay cables control method.

In the current paper, the ageing and de-ageing phenomena in ferroelectric ceramics are modelled by a Landau-type model based on the internal bias field theory. A new phenomenological term for the internal bias electrical field is added into the free energy function to simulate the phenomenon of lattice symmetry during the ageing phenomenon. The simulations for both ageing and de-ageing phenomena are successfully presented in the current paper. The hysteretic behaviours of the ageing and de-ageing phenomena are captured very well by the proposed model.

The need to estimate the micromechanical properties of elastico-mechanoluminescent (EML) composites was established in Part A of this paper. The particle–matrix interface was identified to be poorly understood towards building accurate EML models and to predict functional life estimates of the EML devices. Towards this, Part A of this paper defined the mechanical behavior of the interface as a softening spring through a bilinear cohesive zone model (CZM). Macroscale stress measurements were combined with material properties to estimate undamaged stiffness of the interface spring ( k σ i n t ). In Part B of this paper, the damage characteristics of the interface spring are estimated through an experimental approach to complete the CZM. This is achieved by first establishing the finite strain behavior of the macroscopic EML–PDMS composite from uniaxial tensile testing. Secondly, a controlled tear is induced in the composite and the microscale displacement fields around the tear tip are captured using digital image correlation technique. Tear tip displacements and finite strain behavior are combined to estimate cohesive stresses in the tear-tip region of the composite. The contribution of particle–matrix interfaces towards resisting propagation of the tear is isolated from experimental results to obtain interface-CZM damage parameters. The interface CZM parameters are subsequently utilized in an FEM model to simulate macroscopic composite behavior to find good correlation. The experimental framework established in this paper can be utilized to estimate interface parameters of any particulate-elastomer composites that exhibit finite strain behavior.

The multiphysics model of ionic polymer-metal composite (IPMC) sensors proposed by Zhu has a significant advantage of being able to describe the dynamic sensor response, which highly depends on humidity, by explicitly considering solvent dynamics. However, it is difficult to perform analysis and simulation because Zhu’s model is represented by complex non-linear partial differential equations. This paper describes the symbolic finite element discretization of Zhu’s model and further discusses the essential dynamics of the reduced-order model extracted from the finite element model. The obtained linear ordinary differential equations, or the state equation, can be easily implemented in simulators via common programming languages. The simulation results of an in-house simulator implemented by MATLAB code show good agreement with those of direct numerical simulation by using commercial software, COMSOL. To further simplify the model, the minimum order required for an appropriate approximation is numerically investigated by using a model order reduction technique. This paper reveals that the dynamic response of an IPMC sensor can be consequently approximated by a first-order or second-order linear time-invariant system.

With the development of electric vehicles, the energy harvesters of vehicle’s suspensions have been widely investigated. However, most of the existing energy harvesters have replaced the original damper of the suspensions, which reduces vehicle safety. This paper proposes a magnetic energy-harvesting suspension (MEHS) for vehicles, with the advantages of high vehicle safety and a compact structure, which consists of a passive suspension and a harvester. In this paper, the working principle and the structure of the MEHS are introduced. To better analyze the magnetic field, the magnetic flux circuit model is established by combining the magnetic field division method with the magnetic equivalent circuit model. Furthermore, a dynamic model for a two-degree-of-freedom quarter-vehicle with the MEHS is built to analyze the energy-harvesting characteristics and the damping characteristics. A prototype of the quarter-vehicle that is considering the tire stiffness, is designed and manufactured, and the performances are investigated by simulations and experiments with different frequencies, external resistances and amplitudes. The experimental results indicate that the harvested peak power of the MEHS is 1.08 W with a sinusoidal input of 10 Hz and 2 mm. Moreover, the maximum energy-harvesting efficiency of the prototype reaches 67% at the sinusoidal input of 6 Hz and 2 mm. The harvested energy of the MEHS can power some electrical equipment of vehicles.

The sensitivity of the electronic properties of carbon nanotubes to gases, chemicals, temperature, and mechanical strain enables their use as fillers in nanocomposites for sensing applications. In this paper, the authors develop a low-cost and scalable process based on inkjet printing technology to fabricate printed flexible sensors used for strain and damage detection. A well-dispersed conductive water-based ink is fabricated with functionalized multiwall carbon nanotubes (MWCNT) and deposited onto paper and Kapton substrates to obtain a sheet resistance as low as 500 Ω/sq with about 30 printed layers. The number of printed layers, the direction of the electrical resistance measurement, and the type of substrate have clear effects on the sensor's electrical performances related to the detection of mechanical strain and impact damage. This work demonstrates the effectiveness of the printed sensors for micrometeoroid and orbital debris (MMOD) impact damage detection through hypervelocity testing.

The paper proposes a new hybrid approach technique to simulate acousto-ultrasonic wave excitation and propagation due to operation of the partially debonded piezoelectric transducer attached to a plate-like structure. The semi-analytical boundary integral equation method is applied to calculate guided waves propagation in the unbounded structures and to separate different guided waves in the piezo-induced wave-fields. The obtained model is verified experimentally using the scanning laser Doppler vibrometry. Eigenfrequencies are calculated and analysed for various sizes of the transducer and for different bonding conditions between the transducer and the waveguide. The impact of the transducer’s height, size and debonding area on symmetric and antisymmetric Lamb waves excitation is analysed. The paper demonstrates that one-sided debonding of the transducer exerts intense influence on the distribution of the wave energy among the excited Lamb wave modes, while center debonding has a sizable impact only at relatively high frequencies.

The purpose of this study was to produce a kirigami inspired split ring resonator (SRR) strain sensor. Since the SSR resonance frequency depends strongly on its split gap, one kirigami cut was designed to align with the SSR split gap, allowing SSR resonance frequency to be varied by applying tensile stress. The relationship between frequency and induced strain helps to explain the strain sensing mechanism. Two sheets of paper were used as the dielectric for compatibility with the kirigami technique, and a conductive pattern was inkjet printed on the top paper using silver nanoparticle ink, whereas the ground plane on the bottom paper was inkjet printed using stretchable ink. The two papers were bonded using epoxy strain sensor and S parameters for the fabricated sensor were measured at different strain levels. Resonance frequency increased from 4 to 4.64 GHz for 17.24% applied strain, with measured strain sensitivity = 4.2 × 107 Hz/%, and minimum detectable strain level ≈ 0.84%. Measurement results were compared with simulation results. The proposed strain sensor is relatively easy to manufacture, low cost, and disposable because it was inkjet printed on paper.

This paper presents a novel capacitive pressure sensor that is capable of making highly accurate measurements at low pressure. Different from the method that many researchers have successfully used to improve the sensitivity of capacitive sensors by using a micro-structured dielectric layer (such as the micro-structured PDMS film), this paper creatively used an elastic metallized sponge (nickel-plated polyurethane sponge) as the elastic porous electrode of the capacitive sensor, so that it can detect very low pressure (such as a 0.2 g soybean). Compared with the traditional capacitive sensor using an insulative polyurethane sponge as the dielectric, the baseline capacitance of the sensor of the same size can increase by 10 times, and it has a better signal-to-noise ratio. In addition, the sensor has good robustness due to the good mechanical properties of the nickel-plated polyurethane sponge. The fabrication process of the sensor is extremely simple, the cost is low, and it can be made into any planar shape. In this paper, we describe the structure, principle and manufacture of the sensor, and present the application on robotic grasping.

In this paper, soft pottery was utilized for the first time as the triboelectric material to prepare a triboelectric nanogenerator (SP-TENG), and the triboelectric polarity of soft pottery was demonstrated through a series of experiments, which can get electrons during the triboelectrification process. Some commercial materials, such as nylon, conductive copper tape, and paper card, were made as the triboelectric pair, conductive electrode, and supporting structure, respectively. According to the results, the approximate values of open circuit voltage (Voc) can extend to 179 V, and the short-circuit current (Isc) can reach 5 μA. To demonstrate the generated electrical output of SP-TENG, an electronic calculator and 54 green high-power light-emitting diodes (LEDs) can be easily powered. This research demonstrated the feasibility to utilize recyclable material to prepare TENG for harvesting energy, which could facilitate the wide and sustainable workable application of TENGs.

This article presents an improved nonlinear ultrasonic technique for fatigue damage detection utilizing a kind of carefully designed aluminum-lead composite metamaterial. It focuses on developing a bandgap metamaterial to improve the accuracy and identifiability of the superharmonic features from fatigue cracks by eliminating the inherent nonlinear components in the nonlinear ultrasonic technique. The study starts with the unit cell design through modal analysis by applying the Bloch–Floquet boundary condition to obtain the band structure. Based on the local resonance mechanism, by adjusting the height ratio between the aluminum and lead cylinders, the bandgaps covering the required frequency ranges can be opened up. Then, a chain of regularly arranged unit cells is modeled to analyze the spectral response and verify the bandgap effect through harmonic analysis. The targeted ultrasonic frequency component of guided waves within the bandgap can be mechanically filtered out. Subsequently, a finite element model of the pitch-catch active sensing procedure for fatigue crack detection is constructed via the coupled-field transient dynamic analysis. Nonlinear ultrasonic experiments with the designed metamaterial are carried out to verify the theoretical and numerical investigations. This paper demonstrates that the metamaterial, with its outstanding wave manipulation capability, shows great potential on structural health monitoring and nondestructive evaluation applications. The paper finishes with summary, concluding remarks, and suggestions for future work.

This paper reports on the design, modelling and measured response of a high frequency vibration energy harvester that uses relaxor ferroelectric transduction. The ultimate goal is to build a harvester capable of extracting energy from the kilohertz frequency vibrations associated with the gear meshing-frequencies of a Bell 206B-1 Kiowa helicopter main rotor transmission. During operation the transmission oil temperature is 80°C–100°C. The harvester will be mounted externally to the transmission casing and is expected to operate at elevated temperatures. The prototype harvester reported in this paper uses a [011]c cut PIN-PMN-PT single crystal transducer configured for operation in d 32 transverse extension mode. Modelling was done by adapting an existing lumped element mathematical model to include the d 32 transducer orientation, from which an analytical transfer function was developed. The temperature dependence of the piezoelectric charge constant, d 32, the transducer capacitance, C, and the change in short circuit stiffness were measured from room temperature to 100°C for input into the model. The model predictions were compared to measured output of a prototype harvester over load resistances in the range 10 kΩ–10 MΩ, and shown to be valid for predicting voltage and power levels for loads under 1 MΩ. The model was used to optimise the design of the harvester, and predicts that the optimised design will generate a maximum average output power of 210 mW while operating at 100°C and driven by the measured Bell 206B-1 Kiowa main transmission vibrations near 1900 Hz.

Inorganic ferroelectrics which have low tensile strength and poor ductility are difficult to be bent. In this paper, in order to realize great toughness, the inorganic ferroelectric film was deposited on flexible muscovite (Mica) substrate. For efficiency and convenience, sol-gel method is adopted to fabricate the Bi3.15Nd0.85Ti3O12 (BNT) thin-film capacitor on flexible Mica substrate with SrRuO3 (SRO) electrode layer. The remnant polarization of the Pt/BNT/SRO/CFO/Mica capacitor achieves ~38 μC cm−2, which is larger than most BNT films prepared on hard substrates. No obvious fatigue phenomenon is observed for the BNT capacitor with 1010 switching cycles. The most important is that the Pt/BNT/SRO/CFO/Mica capacitor still owns relatively stable electrical properties when it is bent to 5 mm radius, showing an excellent bending performance for this structure. The flexible, anti-fatigue ferroelectric capacitor prepared in this paper is expected to get a wide range of application in flexible logic and elements for information storage, data processing and communication.

The piezoelectric-driven noncontact jetting dispenser with the characteristics of high accuracy, efficiency and applicability has been widely applied in the microelectronics packaging field to produce small droplets. The process of droplet formation and separation is the key to successful jetting. In order to study the process and show the roles of system parameters in droplet formation, the paper runs some numerical simulations and analyzes the comprehensive effects of the system parameters on the morphological change of droplets by using two dimensionless parameters Weber and Reynolds. The simulation and experiment results show that the scale of system parameters is confirmed by the lower and upper limits of Weber according to different Reynolds. If Weber is bigger than the upper limit value or smaller than the lower limit value, the jetting failure like sputtering, satellite dots jetting or adhesion will occur. During the experiments, the system parameters should be adjusted to keep the values of Weber and Reynolds in the proposed scale. The findings in this paper can be used to guide the design and control of these piezoelectric driven dispensers.

In this paper, the effects of flexoelectricity and strain gradient elasticity on Lamb waves propagating in an infinite piezoelectric nanoplate are analytically investigated. The dispersion equations are obtained and numerically solved for both the electrically open and short cases. A detailed discussion about the dispersion relations of the lowest mode is subsequently presented. Numerical results indicate that flexoelectricity and strain gradient elasticity have a substantial effect on Lamb wave propagation. Compared with the phase velocity of classical piezoelectric Lamb waves, flexoelectricity could decrease the phase velocity, while strain gradient elasticity could increase it. The effects of flexoelectricity and strain gradient elasticity largely depend on the wave number, material properties and nanoplate thickness. In infinite PZT-5H ceramic nanoplates, the effects of flexoelectricity and strain gradient elasticity on the phase velocity are negligible for wave numbers less than 106 m−1. However, for larger wave numbers, not only the phase velocity but also the dispersion relations can be significantly changed with the introduction of flexoelectricity and strain gradient elasticity. In addition, the effects of flexoelectricity and strain gradient elasticity on the electromechanical coupling coefficient are significant and complicated. Since the flexoelectric effect and the strain gradient elasticity effect exist in almost all dielectric materials, the conclusions obtained in this paper are general and can be applied to the analysis and design of the acoustic devices based on Lamb wave propagation.

A micro cantilever (MC) and a probe are two main components of the atomic force microscope (AFM). The dimensions of these components are in micro scales while their oscillation amplitude is on a nanometer scale. The present study intended to not only increase the accuracy of the simulation with regard to geometric discontinuities based on the Timoshenko beam model using the modified couple stress (MCS) theory but also increase the accuracy of the prediction of a system behavior by considering the hysteresis effect into the system vibration equations based on Bouc–Wen model. Since, the classical theory disregarded the molecular structure of matter and neglected the microstructure size dependency, which raise its physical breakdowns in micro and nanoscale applications. Therefore, some micro continuum theories are developed to account for the microstructure effects by introducing additional material constants to the conventional ones. Due to the lack of the experimental results for this kind of MCs, this paper is focused on the both experimental and simulation results by utilizing the DMASP MC. The roughness of the surfaces affects the MC vibration behavior in the air medium. Therefore, surface roughness affecting van der Waals force has been considered in the air medium. Furthermore, the simulation results are compared with experimental results in the air medium with different moisture content during the surface topography. Due to the results, the best surface topography is achieved in the third vibration mode. Since the piezoelectric MC can tolerate the limited voltage, for this AFM MC type, the best surface topography is achieved in the third mode. Hence, this paper highly recommends using the third vibration mode during the surface topography. Finally, based on the EFAST method the most effective parameters on the AFM MC performance are the piezoelectric layer length, thickness and the probe length.

This paper presents intensive studies on the strain rate-, hold time-, and temperature-dependent cyclic behaviors of amorphous shape memory polymers (SMPs). The cyclic characteristics play a vital role in the application of SMPs since the materials suffer cyclic loadings commonly in engineering. A multi-branch fractional derivative model is employed in the paper to investigate the complicated mechanisms underlying the cyclic behaviors. And a modified Eying model is incorporated with the fractional derivative model to describe the temperature-dependent yielding and post-yielding behaviors. A rate-dependent yielding factor is proposed in the study to depict the influence of strain rates. The validity and adaptability of the model are verified through comparisons between the simulations and experimental results of two different materials subjected to different loading conditions. In addition, detailed parameter studies provide effective suggestions on improving the performance of SMPs under various conditions.

The application and characterization of thermal interface material (TIM) for vibrational structures is investigated in this paper. The vibrating feature during the operation requires unique solution for its thermal management, since the connection between the device and heat dissipater should be able to conduct heat efficiently and impose minimum constraint onto the vibration simultaneously. As a typical vibrational device, piezoelectric transformers (PTs) are discussed in this paper. The PTs have urgent demands for thermal dissipation since their power conversion efficiency decrease rapidly with the rising temperature. A novel method by applying vertically aligned carbon nanotube (VACNT) arrays to the interface between PT and heat dissipater is presented to enhance the performance of piezoelectric transformers. VACNT arrays are one of the excellent TIMs. It can directly establish thermal contact between two surfaces by van der Waals' forces. In addition, the unique anisotropic character of CNT arrays provides enough flexibility to accommodate the vibration during the operation. Different configurations of TIMs are compared with each other in this work, including CNT arrays, tape of polypropylene (PP) membrane and without heat transfer structure (HTS). The results indicate that the temperature rise is lowest and the efficiency is highest at the same power density while CNT arrays served as the TIM. Almost no significant fretting and wearing damage occurred on PT electrode surface with CNT arrays TIM even after working continuously for 120 days. Meanwhile, the thermo-physical properties of CNT arrays at contact interface are measured by optical transient thermo-reflectance technique.