Table of contents

Little published data exists on the behavior of MR fluids in squeeze mode. Many of the basic properties of MR fluids in squeeze mode are still unknown. In squeeze mode, MR fluids can generate a large range of force associated with a small displacement. As a result, squeeze mode has recently received more attention. This research focuses on modeling and testing MR fluids in squeeze mode. A novel squeeze mode rheometer is designed and built. MR fluid is tested in squeeze mode to evaluate its performance and behavior. The rheometer can test MR fluid under different conditions (gap size, magnetic field density, speed, etc). It utilizes a Gauss meter for direct measurement of the magnetic field density. MR fluid squeeze test results show that MR fluid can deliver a large range of force that is comparable in magnitude to the force in shear mode. The tests also indicate a clumping effect of the fluid when tested in repeated cycles that does not appear to have been documented previously. This paper describes, in detail, the clumping effect and provides possible reasons for this phenomenon. A non-dimensional mathematical model is developed and validated experimentally. The non-dimensional model directly compares the squeeze mode force to the shear mode force. The results indicate that MR fluid in squeeze mode can be used in many applications requiring a large range of controllable force in envelopes that can only accommodate small strokes.

The design and fabrication of a wireless, passive flow sensor based on changes in magnetic higher-order harmonic fields is described. The sensor consisted of a flow channel, a permanent magnetic strip (biasing element) and a magnetically soft ferromagnetic strip (sensing element). The biasing element was attached on the channel's wall in parallel to the flow direction, while the sensing element was applied on the opposite wall at a small angle to the flow direction. Flowing water in the channel created a pressure on the sensing element's surface, causing a deflection that varied its separation distance from the biasing element. The change in the separation distance in turn altered the biasing field experienced by the sensing element, causing a shift in its higher-order harmonic fields that could be measured remotely through a magnetic coil. The novelty of this sensor is its wireless, passive nature, which is ideal for applications where wire connections are prohibited. In addition, this sensor can be used on a disposable basis due to its simple design and relatively low material cost.

The response of active–passive–constrained layer beams is examined via the use of quasi-two-dimensional finite element formulation. Passive damping in the system is provided by a viscoelastic layer, and a piezoelectric actuation layer is used to achieve active damping. The quasi-two-dimensional finite element formulation allows through-the-thickness representation of the field variables via polynomials and their interpolation along the span by Lagrange cubic elements. The formulation is compared with the conventional formulation via numerical simulations. The response magnitudes predicted using the conventional formulation are higher than those obtained using the present formulation for systems with high core thickness, while approximately identical magnitudes are predicted for systems with low core thickness. Specific to the present quasi-two-dimensional formulation, the application of a cantilevered boundary condition to the three layers yields the same response as would have been obtained by enforcing the clamped condition on just the top and bottom layers of the cantilevered end.

The objective of this research is to investigate the feasibility of utilizing the hybrid method of ensemble empirical mode decomposition (EEMD) and pure empirical mode decomposition (EMD) to efficiently decompose the complicated vibration signals of rotating machinery into a finite number of intrinsic mode functions (IMFs), so that the fault characteristics of the misaligned shaft can be examined in the time–frequency Hilbert spectrum as well as the marginal Hilbert spectrum. The intrawave frequency modulation (FM) phenomenon, which indicates the nonlinear vibration behavior of a misaligned shaft, can be observed in the time–frequency Hilbert spectrum through the Hilbert–Huang transform (HHT) technique. The fault characteristic of shaft misalignment is also featured in terms of the amplitude modulation (AM) phenomenon in the information-containing IMF components that are extracted by the significance test. Through performing the envelope analysis on the information-containing IMF, the marginal Hilbert spectrum of the envelope signal of this IMF component exhibits that the level of shaft misalignment is presented by the level of AM in the IMF. A test bed of a rotor-bearing system is performed experimentally to illustrate both the parallel and angular shaft misalignment conditions as well as the healthy condition. The analysis results show that the proposed approach is capable of diagnosing the misaligned fault of the shaft in rotating machinery and providing a more meaningful physical insight compared with the conventional methods.

Magnetorheological (MR) elastomers are used to construct a smart sandwich beam for micro-vibration control. The micro-vibration response of a clamped–free sandwich beam with an MR elastomer core and a supplemental mass under stochastic support micro-motion excitation is studied. The dynamic behavior of MR elastomer as a smart viscoelastic material is described by a complex modulus which is controllable by external magnetic field. The sixth-order partial differential equation of motion of the sandwich beam is derived from the dynamic equilibrium, constitutive and geometric relations. A frequency-domain solution method for the stochastic micro-vibration response of the sandwich beam is developed by using the frequency-response function, power spectral density function and spatial eigensolution. The root-mean-square velocity response in terms of the one-third octave frequency band is calculated, and then the response reduction capacity through optimizing the complex modulus of the core is analyzed. Numerical results illustrate the influences of the MR elastomer core parameters on the root-mean-square velocity response and the high response reduction capacity of the sandwich beam. The developed analysis method is applicable to sandwich beams with arbitrary cores described by complex shear moduli under arbitrary stochastic excitations described by power spectral density functions.

This paper deals with the shape control of a cantilever beam structure by using laminated piezoelectric actuators (LPAs) with a low control voltage. The shape control equation of the cantilever beam partially covered with LPAs is derived based on the constitutive relations of the elastic material and piezoelectric material and shear deformation beam theory (Timoshenko theory). The actuating forces produced by the LPAs are formulated as well. It reveals how the actuating forces depend on the number of piezoelectric layers, the thickness of piezoelectric layers and the position of the actuators. The driving voltages of the LPAs are then determined by a genetic optimization algorithm. The shape control of the cantilever beam from applying the optimal voltage to the LPAs is simulated. The simulation results show that an LPA of large layer number is able to diminish effectively the pre-deflection of the beam under a low control voltage. The voltage applied to the LPA of five layers was almost five times smaller than that of one layer. In addition, increasing the number of LPA layers can significantly improve the control performance as the acting forces of the LPA are a quadratic function of the LPA layer number. The L² norm of the displacement array of all nodes is diminished about 30% after optimization. Also with the same low control voltage, the LPA can obtain a better control performance than the conventional single layer piezoelectric actuator.

Polyaniline (PANI) is an important electrorheological (ER) material. In this paper, PANI with different morphologies, including nanofiber, nanoparticle and microparticle, are prepared on a large scale by a simple and modified oxidative polymerization method in a low-cost citric acid aqueous solution. The effect of particle morphology on the electric, ER, sedimentation, and temperature properties of PANI suspensions is investigated systematically. The results show that the suspensions containing PANI nanofibers and nanoparticles possess significantly improved suspended stability compared to the suspension containing PANI microparticles. Under electric fields, however, the PANI nanofiber suspension exhibits the strongest ER effect. Its yield stress is about 2.5–3.0 times as high as that of the PANI nanoparticle suspension and 1.3–1.5 times as high as that of the PANI microparticle suspension. The shear stress of the PANI nanofiber suspension maintains this more stable level in the wide shear rate region of 0.1–1000 s⁻¹ as compared to that of the PANI nanoparticle and microparticle suspensions. Furthermore, the temperature test shows that the PANI nanofiber suspension can maintain a good ER effect in a wide temperature range like the PANI microparticle suspension, while the temperature stability of the PANI nanoparticle suspension is reduced, possibly due to smaller particle size.

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.

This paper presents the development of an autonomously powered and controlled robotic fish that incorporates an active flexural joint tail fin, activated through conducting polymer actuators based on polypyrrole (PPy). The novel electromaterial muscle oscillator (NEMO) tail fin assembly on the fish could be controlled wirelessly in real time by varying the frequency and duty cycle of the voltage signal supplied to the PPy bending-type actuators. Directional control was achieved by altering the duty cycle of the voltage input to the NEMO tail fin, which shifted the axis of oscillation and enabled turning of the robotic fish. At low speeds, the robotic fish had a turning circle as small as 15 cm (or 1.1 body lengths) in radius. The highest speed of the fish robot was estimated to be approximately 33  mm s⁻¹ (or 0.25 body lengths s⁻¹) and was achieved with a flapping frequency of 0.6–0.8 Hz which also corresponded with the most hydrodynamically efficient mode for tail fin operation. This speed is approximately ten times faster than those for any previously reported artificial muscle based device that also offers real-time speed and directional control. This study contributes to previously published studies on bio-inspired functional devices, demonstrating that electroactive polymer actuators can be real alternatives to conventional means of actuation such as electric motors.

Polyaniline thin films, doped with an inorganic acid (HCl), on glass and Si substrates were directly synthesized by an in situ polymerization technique. Studies on the surface morphology as well as topography proved that the film surface is evolved differently on different substrates. The formation of PANI on glass and Si substrates was confirmed by optical and infrared spectroscopy, respectively. Different surface characteristics for different substrates showed a strong effect on the gas sensing properties of these films. The porous fibril morphology on the Si substrate leads to significantly faster and more responsive sensing phenomena.

A quasi-static (low frequency) model is developed for THUNDER actuators configured as displacement sensors based on a simple Raleigh–Ritz technique. This model is used to calculate charge as a function of displacement. Using this and the calculated capacitance, voltage versus displacement and voltage versus electrical load curves are generated and compared with measurements. It is shown that this model gives acceptable results and is useful for determining rough estimates of sensor output for various loads, laminate configurations and thicknesses.

We investigate the effect of viscous dissipation on the dispersive and attenuated characteristics of SH surface acoustic wave propagation in a layered piezoelectric structure, which consists of a thin functionally graded piezoelectric material (FGPM) layer bonded perfectly to an unbounded elastic substrate. The piezoelectric material is polarized in z-axis direction and the material properties change gradually along the thickness of the layer. The solutions of the dispersion relations are obtained for electrically open or shorted conditions by means of the transfer matrix method. The effects of the gradient variation of material constants on the phase velocity and attenuation are presented and discussed in detail. The analytical method and results can be useful for the design of resonators and sensors.

The heating of shape memory alloy (SMA) materials leads to a thermally driven phase change which can be used to do work. An SMA wire can be thermally cycled by controlling electric current through the wire, creating an electro-mechanical actuator. Such actuators are typically heated electrically and cooled through convection. The thermal time constants and lack of active cooling limit the operating frequencies. In this work, the bandwidth of a still-air-cooled SMA wire controlled with a PID controller is improved through optimization of the controller gains. Results confirm that optimization can improve the ability of the actuator to operate at a given frequency. Overshoot is observed in the optimal controllers at low frequencies. This is a result of hysteresis in the wire's contraction–temperature characteristic, since different input temperatures can achieve the same output value. The optimal controllers generate overshoot during heating, in order to cause the system to operate at a point on the hysteresis curve where faster cooling can be achieved. The optimization results in a controller which effectively takes advantage of the multi-valued nature of the hysteresis to improve performance.

During the last decade, it was discovered that the mechanical properties and interactions of cells and their surrounding extra-cellular matrix play important roles in cellular activities. Substantial efforts have been made to develop various methodologies and tools to study cell mechanics. In this paper, we report an ongoing study on integrating the concept of a smart structure with a microfabricated thin film piezoelectric transducer for characterizing the various changes in mechanical properties associated with cellular events. A microbridge sensor integrated with a thin film piezoelectric transducer was created from silicon dioxide and zinc oxide sandwiched between two gold electrodes. The cells to be tested were cultured on the microbridge surface. The surface tractions exerted by the cells on the microbridge directly modulated the selected resonant behaviors, which were detected with the custom designed effective surface electrode. Our theory and simulation results showed, for the first time, that the application and changes in these surface tractions resulted in resonant and anti-resonant frequency shifts in the impedance response of the piezoelectric transducer. Both spatial and temporal information of dynamic cellular activities could be inferred from the changes in the impedance spectra. The design, theory, finite-element simulation, microfabrication techniques, and preliminary test results are discussed.

This paper discusses the development of a high speed magnetostrictive mirror deflector that is compact, power efficient, and requires only low voltage for excitation. The magnetostrictive mirror deflector was designed and fabricated, and its performance tested. Three kinds of experiments were conducted to evaluate the performance, namely, identification of resonance frequencies, measurement of the angle of deflection, and study of the stability of the actuator under continuous use. The measurements were made using a high speed charge coupled device camera integrated with a PC using a custom made data acquisition and analysis program. The deflector was able to produce more than 6.1 mrad at 5.28 kHz with a minimal power of 0.8 W. Experiments conducted to test the repeatability of the measurements made have shown that the device is suitable for continuous duty operation. The results obtained in this study showed that the magnetostrictive mirror deflector is a good candidate for lidar and rapidly tunable laser system use.

Shape memory alloy (SMA) has a wide variety of practical applications due to its unique super-elasticity and shape memory effect. It is of practical interest to establish a constitutive model which predicts its phase transformation and mechanical behaviors. In this paper, a new three-dimensional phase transformation equation, which predicts the phase transformation behaviors of SMA, is developed based on the results of a differential scanning calorimetry (DSC) test. It overcomes both limitations: that Zhou's phase transformation equations fail to describe the phase transformation from twinned martensite to detwinned martensite of SMA and Brinson's phase transformation equation fails to express the influences of phase transformation peak temperatures on the phase transformation behaviors of SMA. A new three-dimensional constitutive equation, which predicts the mechanical behaviors associated with the super-elasticity and shape memory effect of SMA, is developed on the basis of thermodynamics and solid mechanics. Results of numerical simulations show that the new constitutive model, which includes the new phase transformation equation and constitutive equation, can predict the phase transformation and mechanical behaviors associated with the super-elasticity and shape memory effect of SMA precisely and comprehensively. It is proved that Brinson's constitutive model of SMA can be considered as one special case of the new constitutive model.

The nature of interfaces between water and hydrophobic materials has been a subject of great interest. Experimental results from tetraethoxysilane (TEOS) based hydrophobic silica films synthesized by the two step sol–gel process using hexadecyltrimethoxysilane (HDTMS) as a co-precursor are described. The molar ratio of TEOS, methanol (MeOH), acidic water (0.001 M, oxalic acid), and basic water (8 M, NH₄OH) was kept constant at 1:66.66:6.76:6.66, and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 22.9 × 10⁻². The maximum contact angle of 125° was obtained for M = 22.9 × 10⁻². It is observed that the water contact angle value on the HDTMS modified films remained stable at 125°, after heat treatment up to 235 °C. However, the water contact angle value decreased to 52° in the case of unmodified films, indicating the improvement in the thermal stability using HDTMS as a co-precursor. The hydrophobic silica films retained their hydrophobicity up to a temperature of 235 °C and above this temperature the films became hydrophilic. The hydrophobic silica films were characterized by surface roughness studies, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, contact angle measurements, and % optical transmission.

1–3 cement-based piezoelectric composite has been developed for health monitoring of concrete structures. Transducers made of this type of composite have broadband frequency response. Plain concrete and engineered cement composite (ECC) beams with embedded 1–3 cement-based piezoelectric transducers were prepared and tested. During experiments, the transducers were used to perform active and passive detection of the damage evolution of the beams. In active detection, a damage index based on the average energy of the received waves was proposed and used. In passive detection, acoustic emission (AE) events were recorded and the accumulated AE event number was analyzed with the loading history. Crack localization was also accomplished in the passive monitoring. The results of the two methods demonstrated similar trends in interpreting the damage evolution of the concrete beam. The results were also consistent with each material's characteristics.

This paper presents a magnetization model that endeavors to capture the change in the rheological behavior due to the application of magnetic fields to ferrofluids (FFs) and magnetorheological fluids (MRFs). Samples of Ferrotec APG 2115 FF and Lord MRF-122-2ED MRF have been tested using an Anton Paar MCR 501 rotational rheometer fitted with a parallel-plate measuring system. On the basis of the results, the FF has been modeled using the Newtonian model whereas the MRF has been adjusted using the Bingham and Herschel–Bulkley models. All three models have been extended using the herein-proposed magnetization model, that provides good adjustment of any of the models to the entire range of applied magnetic field.

This paper deals with automatic valve condition classification of a reciprocating processor with seeded faults. The seeded faults are considered based on observation of valve faults in practice. They include the misplacement of valve and spring plates, incorrect tightness of the bolts for valve cover or valve seat, softening of the spring plate, and cracked or broken spring plate or valve plate. The seeded faults represent various stages of machine health condition and it is crucial to be able to correctly classify the conditions so that preventative maintenance can be performed before catastrophic breakdown of the compressor occurs. Considering the non-stationary characteristics of the system, time–frequency analysis techniques are applied to obtain the vibration spectrum as time develops. A data reduction algorithm is subsequently employed to extract the fault features from the formidable amount of time–frequency data and finally the probabilistic neural network is utilized to automate the classification process without the intervention of human experts. This study shows that the use of modification indices, as opposed to the original indices, greatly reduces the classification error, from about 80% down to about 20% misclassification for the 15 fault cases. Correct condition classification can be further enhanced if the use of similar fault cases is avoided. It is shown that 6.67% classification error is achievable when using the short-time Fourier transform and the mean variation method for the case of seven seeded faults with 10 training samples used. A stunning 100% correct classification can even be realized when the neural network is well trained with 30 training samples being used.

This paper presents an innovative design platform of a piezoelectric energy harvester (EH), called a segment-type EH, and its application to a wireless sensor. Energy harvesting technology is motivated to minimize battery replacement cost for wireless sensors, which aims at developing self-powered sensors by utilizing ambient energy sources. Vibration energy is one of the widely available ambient energy sources which can be converted into electrical energy using piezoelectric material. The current state-of-the-art in piezoelectric EH technology mainly utilizes a single natural frequency, which is less effective when utilizing a random ambient vibration with multi-modal frequencies. This research thus proposes a segment-type harvester to generate electric power efficiently which utilizes multiple modes by separating the piezoelectric material. In order to reflect the random nature of ambient vibration energy, a stochastic design optimization is solved to determine the optimal configuration in terms of energy efficiency and durability. A prototype is manufactured and mounted on a heating, ventilation, air conditioning (HVAC) system to operate a temperature wireless sensor. It shows its excellent performance to generate sufficient power for real-time temperature monitoring for building automation.

Household assistance robots are expected to become more prominent in the future and will require inherently safe design. Conducting polymer-based artificial muscle actuators are one potential option for achieving this safety, as they are flexible, lightweight and can be driven using low input voltages, unlike electromagnetic motors; however, practical implementation also requires a scalable structure and stability in air. In this paper we propose and practically implement a multilayer conducting polymer actuator which could achieve these targets using polypyrrole film and ionic liquid-soaked separators. The practical work density of a nine-layer multilayer actuator was 1.4 kJ m⁻³ at 0.5 Hz, when the volumes of the electrolyte and counter electrodes were included, which approaches the performance of mammalian muscle. To achieve air stability, we analyzed the effect of air-stable ionic liquid gels on actuator displacement using finite element simulation and it was found that the majority of strain could be retained when the elastic modulus of the gel was kept below 3 kPa. As a result of this work, we have shown that multilayered conducting polymer actuators are a feasible idea for household robotics, as they provide a substantial practical work density in a compact structure and can be easily scaled as required.

This paper proposes a novel approach for controlled pushing of a micro-sized object along a desired path. Challenges associated with this control task due to the presence of dominating micro-forces are carefully studied and a solution based on the application of artificial neural networks is introduced. A nonlinear controller is proposed for controlled pushing of micro-objects which guarantees the stability of the closed-loop system in the Lyapunov sense. An experimental setup is designed to validate the performance of the proposed controller. Results suggest that artificial neural networks present a promising tool for design of adaptive controllers to accurately manipulate objects in the microscopic scale.

Silicone is a common dielectric elastomer material. Actuators made from it show excellent activation properties including large strains (up to 380%), high energy densities (up to 3.4 J g⁻¹), high efficiency, high responsive speed, good reliability and durability, etc. When a voltage is applied on the compliant electrodes of the dielectric elastomers, the polymer shrinks along the electric field and expands in the transverse plane. In this paper, a silicone dielectric elastomer is synthesized and the area strains are tested under different electric fields. Pre-strain and a certain driving electric field are applied to the film and the induced large strain by the Maxwell stress is measured. Barium titanate (BaTiO₃) was incorporated into the silicone to fabricate a new dielectric elastomer: the experimental results show that the elastic modulus and dielectric constant were significantly improved. The experimental results coincide well with those of finite element analysis at a large deformation. Also, a theoretical analysis is performed on the coupling effects of the mechanical and electric fields. A nonlinear field theory of deformable dielectrics and hyperelastic theory are adopted to analyze the electromechanical field behavior of these actuators. Also the mechanical behavior of the dielectric elastomer undergoing large free deformation is studied. Finally, the constitutive model of a dielectric elastomer composite under free deformation and restrained deformation is derived.

In order to make full use of the controllable damping characteristics of magnetorheological (MR) dampers, feedback control of the damping forces for MR dampers is necessary, which needs extra dynamic response sensors and control systems as active control systems do. The extra dynamic response sensors for semi-active control of the MR dampers will increase the application cost of MR dampers, occupy the installation space, complicate the system, and decrease the reliability. In this paper, an integrated relative displacement sensor (IRDS) technology to make MR dampers self-sensing based on electromagnetic induction, and the principle of an integrated relative displacement self-sensing MR damper (IRDSMRD) based on the IRDS technology, are introduced. The IRDSMRD mainly comprises an exciting coil wound on the piston and an induction coil wound on the nonmagnetic cylinder. In the IRDSMRD, the coil wound on the piston simultaneously acts as the exciting coils of the MR fluid and the IRDS while the coil wound on the cylinder acts as the induction coil of the IRDS. The MR fluid in the annular fluid channel and the IRDS are simultaneously energized by the exciting coil through letting the carrier of the IRDS (AC) possess different frequency from the current for the MR fluid (DC), which realizes the frequency division multiplexing of the exciting coil. Based on the proposed principle for the IRDS and IRDSMRD, an IRDSMRD is designed and modeled and the damping and sensing performances of the designed and developed IRDSMRD are also modeled and analyzed using the finite element method (FEM) with the software package Maxwell 2D. The research results indicate that the function of the relative displacement sensing property can be integrated into MR dampers, and the designed IRDSMRD possesses large controllable damping ratio and good relative displacement sensing performance utilizing the IRDS technology proposed in this paper.

We derive one-dimensional equations for the extension and flexure with shear deformation of a piezoelectromagnetic beam with rectangular cross section from three-dimensional equations. The equations obtained are used to analyze magnetoelectric effects in fibers of piezoelectric/piezomagnetic composites. Both static magnetoelectric effects and frequency-dependent magnetoelectric effects in time-harmonic motions are examined. Various material and field orientations are considered. We also make comparisons between magnetoelectric effects in fibers and in thin films on substrates. Two-dimensional equations for laminated piezoelectric/piezomagnetic plates are used in the analysis of the thin films. It is found that magnetoelectric effects in fibers are significantly stronger than those in thin films on substrates.

The future of space satellite technology lies in ultra-large mirrors and radar apertures for significant improvements in imaging and communication bandwidths. The availability of optical-quality membranes drives a parallel effort for structural models that can capture the dominant dynamics of large, ultra-flexible satellite payloads. Unfortunately, the inherent flexibility of membrane mirrors wreaks havoc with the payload's on-orbit stability and maneuverability. One possible means of controlling these undesirable dynamics is by embedding active piezoelectric ceramics near the boundary of the membrane mirror. In doing so, active feedback control can be used to eliminate detrimental vibration, perform static shape control, and evaluate the health of the structure.

The overall motivation of the present work is to design a control system using distributed bimorph actuators to eliminate any detrimental vibration of the membrane mirror. As a basis for this study, a piezoceramic wafer was attached in a bimorph configuration near the boundary of a tensioned rectangular membrane sample. A finite element model of the system was developed to capture the relevant system dynamics from 0 to 300 Hz. The finite element model was compared against experimental results, and fair agreement found. Using the validated finite element models, structural control using linear quadratic regulator control techniques was then used to numerically demonstrate effective vibration control. Typical results show that less than 12 V of actuation voltage is required to eliminate detrimental vibration of the membrane samples in less than 15 ms. The functional gains of the active system are also derived and presented. These spatially descriptive control terms dictate favorable regions within the membrane domain for placing sensors and can be used as a design guideline for structural control applications. The results of the present work demonstrate that thin plate theory is an appropriate modeling medium for capturing the relevant system dynamics of an active membrane mirror and can be used effectively to set the framework for the closed-loop vibration control architecture.

Ionic polymer metal composites (IPMCs) are electroactive material devices that bend at low applied voltage (1–4 V). Inversely, a voltage is generated when the materials are deformed, which makes them useful both as sensors and actuators. In this paper, we propose two new highly porous carbon materials as electrodes for IPMC actuators, generating a high specific area, and compare their electromechanical performance with recently reported RuO₂ electrodes and conventional IPMCs. Using a direct assembly process (DAP), we synthesize ionic liquid (Emi-Tf) actuators with either carbide-derived carbon (CDC) or coconut-shell-based activated carbon-based electrodes. The carbon electrodes were applied onto ionic liquid-swollen Nafion membranes using a direct assembly process. The study demonstrates that actuators based on carbon electrodes derived from TiC have the greatest peak-to-peak strain output, reaching up to 20.4 mε (equivalent to>2%) at a 2 V actuation signal, exceeding that of the RuO₂ electrodes by more than 100%. The electrodes synthesized from TiC-derived carbon also exhibit significantly higher maximum strain rate. The differences between the materials are discussed in terms of molecular interactions and mechanisms upon actuation in the different electrodes.

Vibration energy harvesting is being pursued as a means to power wireless sensors and ultra-low power autonomous devices. From a design standpoint, matching the electrical damping induced by the energy harvesting mechanism to the mechanical damping in the system is necessary for maximum efficiency. In this work two independent energy harvesting techniques are coupled to provide higher electrical damping within the system. Here the coupled energy harvesting device consists of a primary piezoelectric energy harvesting device to which an electromagnetic component is added to better match the total electrical damping to the mechanical damping in the system. The first coupled device has a resonance frequency of 21.6 Hz and generates a peak power output of ∼332 µW, compared to 257 and 244 µW obtained from the optimized, stand-alone piezoelectric and electromagnetic energy harvesting devices, respectively, resulting in a 30% increase in power output. A theoretical model has been developed which closely agrees with the experimental results. A second coupled device, which utilizes the d₃₃ piezoelectric mode, shows a 65% increase in power output in comparison to the corresponding stand-alone, single harvesting mode devices. This work illustrates the design considerations and limitations that one must consider to enhance device performance through the coupling of multiple harvesting mechanisms within a single energy harvesting device.

This paper presents modelling and analysis of microdiaphragms that are designed for implantable micropump applications. Microdiaphragms are considered to be a major component of micropumps. A securely operated, electrostatically actuated, fully passive micropump is designed using a novel method, which is based on surface acoustic wave (SAW) devices and wireless transcutaneous radio frequency (RF) communication. The device is capable of extracting the required power from the RF signal itself, like RFID (ID: identification device) tags; hence the need of a battery and active electronics is negated. Moreover, a SAW correlator is used for secure interrogation of the device. As a result, the device responds only to a unique RF signal, which has the same code as was implanted in the SAW correlator. Finite element analysis (FEA) based on code from ANSYS Inc. is carried out to model the microdiaphragm, and a Rayleigh–Ritz method based analytical model is developed to investigate the validity of the FEA results. During the FEA, a three-dimensional model of the diaphragm is developed and various kinds of corrugation profiles are considered for enhancing the device performance. A coupled-field analysis is carried out to model the electrostatics–solid interaction between the corrugated microdiaphragm and the SAW device. In modelling microdiaphragms, selection of appropriate material properties and element types, application of accurate constraints, and selection of suitable mesh parameters are carefully considered.

The effect of a linear monomer on thermomechanical properties and shape recovery behavior of an epoxy shape-memory polymer is studied. These shape-memory polymers are prepared from epoxy base resin, hardener and linear epoxy monomer. As the content of the linear monomer increases, the glass transition temperature (T_g) determined using differential scanning calorimetry ranges from 37 to 96 °C. A decrease in rubber modulus is seen from dynamic mechanical analysis for the polymers, which reveals decreasing crosslink density with increasing linear monomer content. Tensile test results show that the elongation at break and strength depends on the content of linear monomer at T_g or T_g−20 °C, while the linear monomer content has minor influence on elongation at break and strength at T_g+20 °C. Finally, investigation on shape recovery behavior reveals that full recovery can be observed for each polymer when the temperature is equal to or above T_g. Also, increasing the linear monomer content results in a decrease in both shape recovery ratio (below T_g) and shape recovery speed (at T_g). These results are interpreted in terms of various crosslink densities attributed to the increasing linear monomer content.

This paper proposes an analytical methodology for the optimal design of a magnetorheological (MR) valve structure. The MR valve structure is constrained in a specific volume and the optimization problem identifies geometric dimensions of the valve structure that maximize the yield stress pressure drop of a MR valve or the yield stress damping force of a MR damper. In this paper, the single-coil and two-coil annular MR valve structures are considered. After describing the schematic configuration and operating principle of a typical MR valve and damper, a quasi-static model is derived based on the Bingham model of a MR fluid. The magnetic circuit of the valve and damper is then analyzed by applying Kirchoff's law and the magnetic flux conservation rule. Based on quasi-static modeling and magnetic circuit analysis, the optimization problem of the MR valve and damper is built. In order to reduce the computation load, the optimization problem is simplified and a procedure to obtain the optimal solution of the simplified optimization problem is presented. The optimal solution of the simplified optimization problem of the MR valve structure constrained in a specific volume is then obtained and compared with the solution of the original optimization problem and the optimal solution obtained from the finite element method.

This paper documents an experimental and theoretical investigation into characterizing the mechanical configurations and performances of THUNDER actuators, a type of piezoelectric actuator known for their large actuation displacements, through fabrication, measurements and finite element analysis. Five groups of such actuators with different dimensions were fabricated using identical fabrication parameters. The as-fabricated arched configurations, resulting from the thermo-mechanical mismatch among the constituent layers, and their actuation performances were characterized using an experimental set-up based on a laser displacement sensor and through numerical simulations with ANSYS, a widely used commercial software program for finite element analysis. This investigation shows that the presence of large residual stresses within the piezoelectric ceramic layer, built up during the fabrication process, leads to significant nonlinear electromechanical coupling in the actuator response to the driving electric voltage, and it is this nonlinear coupling that is responsible for the large actuation displacements. Furthermore, the severity of the residual stresses, and thus the nonlinearity, increases with increasing substrate/piezoelectric thickness ratio and, to a lesser extent, with decreasing in-plane dimensions of the piezoelectric layer.

A conformal load-bearing antenna structure (CLAS) combines the antenna into a composite structure such that it can carry the designed load while functioning as an antenna. In this paper, two types of new 3D integrated microstrip antennas (3DIMAs) with different feeding methods are designed to work at the radar L-band. Different from the conventional CLAS, the radiating patch and the ground plane of the 3DIMA are both composed of woven conductive wires and are bonded into the 3D composite physically by Z-yarns, greatly improving the damage tolerance of the antenna. The return loss of the coaxial-fed antenna is −13.15 dB with a resonant frequency of 1.872 GHz, while that of the microstrip-fed antenna is −31.50 dB with a resonant frequency of 1.33 GHz. Both of the 3DIMAs have similar radiation patterns to that of the traditionally designed microstrip antenna. In addition, an experimental investigation of the impact response of the coaxial-fed 3DIMA was carried out and the results showed the radiation pattern had almost no change even when the antenna received an impact energy of 15 J, exhibiting superior impact resistance to that of a conventional microstrip antenna.

Actuators with high linear-motion speed, high positioning resolution and a long motion stroke are needed in many precision machining systems. In some current systems, voice coil motors (VCMs) are implemented for servo control. While the voice coil motors may provide the long motion stroke needed in many applications, the main obstacle that hinders the improvement of the machining accuracy and efficiency is their limited bandwidth. To fundamentally solve this issue, we propose to develop a dual-stage actuation system that consists of a voice coil motor that covers the coarse motion, and a piezoelectric stack actuator that induces the fine motion, thus enhancing the positioning accuracy. The focus of this present research is the mechatronics design and synthesis of the new actuation system. In particular, a flexure hinge based mechanism is developed to provide a motion guide and preload to the piezoelectric stack actuator that is serially connected to the voice coil motor. This mechanism is built upon parallel plane flexure hinges. A series of numerical and experimental studies are carried out to facilitate the system design and the model identification. The effectiveness of the proposed system is demonstrated through open-loop studies and preliminary closed-loop control practice. While the primary goal of this particular design is aimed at enhancing optical lens machining, the concept and approach outlined are generic and can be extended to a variety of applications.

In this paper, a multi-mode electromagnetic shunt damper employing the current-flowing method is newly developed for the semi-active vibration control of flexible structures. The electromagnetic shunt damper, which is used for the electromagneto-mechanical coupling transduction between vibrating structures and the electrical shunt circuit, consists of a coil and a permanent magnet. The conducting coil is attached to the cantilever beams and the two ends of the coil are connected to the current-flowing shunt circuit for the reduction of vibration. For the analytical and experimental validation of the multi-mode electromagnetic shunt damper, the first two modes of the cantilever beam are semi-actively controlled. In light of the frequency responses, the vibration and damping characteristics of the flexible beams with the electromagnetic shunt damper are investigated with reference to changes in the circuit parameters. Also, the time responses of the integrated systems with an initial condition are experimentally examined for validation of the proposed damper. The effect of the magnetic intensity on the shunt damping is studied by varying the gap between the aluminum beam and the permanent magnet. The theoretical prediction of the frequency response of the electromagneto-mechanically coupled beams shows good agreement with the experimental results. The present results show that the current-flowing electromagnetic shunt damper can be successfully applied to reduce the multi-mode vibration of flexible structures.

In this paper, based on the standard solid model and von Kármán's plate theory, active control of the nonlinear static and dynamic responses for electrically actuated piezoelectric viscoelastic microplates is investigated by applying a purely direct current (DC) voltage and a combined DC voltage and alternating current (AC) voltage. In the former case, the concepts of instantaneous pull-in voltage, durable pull-in voltage, creep pull-in and delay pull-in time are set up. The effect of the controlling voltage on them is also discussed. In the latter case, the effect of the element relaxation coefficient on the free vibration and forced vibration is investigated. The effect of the controlling voltage on them is also shown.

Magnetic gradiometers are powerful tools for mineral exploration. To avoid the problem of heading errors, gradiometers must be made from low susceptibility materials. We compare possible low susceptibility materials for gradiometer use and strategies for minimizing magnetic contamination. In particular, we present the favourable magnetic properties of the advanced engineering plastic Torlon.

Concrete is the most widely used construction material, and carbon nanofibers have many advantages in both mechanical and electrical properties such as high strength, high Young's modulus and high conductivity. In this paper, the mechanical and electrical properties of concrete containing carbon nanofibers (CNF) are experimentally studied. The test results indicate that the compressive strength and per cent reduction in electrical resistance while loading concrete containing CNF are much greater than those of plain concrete. Finally, a reasonable concentration of CNF is obtained for use in concrete which not only enhances compressive strength, but also improves the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete.

Dielectric elastomers are one of the important electroactive polymers used as actuators in adaptive structures due to their outstanding ability to generate very large deformations when subjected to an external electric field. In this paper, the Mooney–Rivlin elastic strain energy function with two material constants is used to analyze the electromechanical stability performance of a dielectric elastomer. This elastic strain energy together with the electric energy incorporating linear permittivity are the main items to construct the free energy of the system. Particular numerical results are also calculated for a further understanding of the dielectric elastomer's typical stability performance. The proposed model offers great help in guiding the design and fabrication of actuators featuring dielectric elastomers.

This paper addresses the problem of designing quantitative feedback theory (QFT) based controllers for the vibration reduction in a structure equipped with an MR damper. In this way, the controller is designed in the frequency domain and the natural frequencies of the structure can be directly accounted for in the process. Though the QFT methodology was originally conceived of for linear time invariant systems, it can be extended to nonlinear systems. A new methodology is proposed for characterizing the nonlinear hysteretic behavior of the MR damper through the uncertainty template in the Nichols chart. The resulting controller performance is evaluated in a real-time hybrid testing experiment.

The NiTi alloy can be trained by repetitive loading or heating cycles. As a result of the training, a two-way shape memory effect (TWSME) can be induced. Considerable research has been reported regarding the TWSME trained by tensile loading. However, the TWSME trained by compressive loading has not been investigated nearly as much. In this paper, the TWSME is induced by compressive loading cycles and the two-way shape memory strain is evaluated by using two types of specimen: a solid cylinder type and a tube type. The TWSME trained by compressive loading is different from that trained by tensile loading owing to the severe tension/compression asymmetry as described in previous research. After repetitive compressive loading cycles, strain variation upon cooling is observed, and this result proves that the TWSME is induced by compressive loading cycles. By performing compressive loading cycles, plastic deformation in NiTi alloy occurs more than for tensile loading cycles, which brings about the appearance of TWSME. It can be said that the TWSME is induced by compressive loading cycles more easily. The two-way shape memory strain increases linearly as the maximum strain of compressive loading cycles increases, regardless of the shape and the size of the NiTi alloy; this two-way shape memory strain then shows a tendency towards saturation after some repeated cycles.

We present the development of a low-temperature liquid composite moulding cure schedule that is compatible with the fabrication of shape memory alloy (SMA)–epoxy composite materials. With this process, the SMA wires do not need to be maintained in place with an external frame, even though the peak post-cure temperature exceeds the activation temperature of the SMA wires. The intrinsic interfacial shear strength of the final material is experimentally determined from single wire pull-out tests, and is compared with the shear stress exerted at the interface by an activated SMA wire. These measurements show that the interface is strong enough to withstand the maximum activation stress. This is confirmed through tests involving the cyclic activation of SMA wires embedded in epoxy samples. The paper successfully demonstrates that, by careful tailoring of the processing schedule, an SMA–epoxy composite that maintains a strong interfacial bond during both processing and subsequent activation of the embedded wires can be fabricated using standard composite processing methods.

A piezoelectric multilamina shell FE developed to model thin walled structures with piezoelectric fibre composites polarized with interdigitated electrodes (PFCPIE) is proposed in this paper. A new scheme for the interpolation of the electric field is presented. The electric field in each lamina lies parallel to the lamina plane and coincides with the poling direction. Each piezoelectric lamina admits an arbitrary poling direction. Based on Reissner–Mindlin assumptions and a multilaminate approach, the element employs a single layer assumption for the mechanical displacements and a layerwise constant electric potential. An MITC strategy is used to avoid shear locking.

Two static examples are presented. The first is a cantilever piezoactuated beam and the second a single cell closed box beam with piezoelectric actuators.

The results obtained for the cantilever beam with the present formulation are compared with those obtained with native ABAQUS plane stress elements and an analytical solution. For the closed box beam the numerical results were compared with experimental results from the literature. Very encouraging results are obtained in both cases.

Finally, for the piezoactuated closed box beam, the FE model is used to obtain a state space model (SS). Based on the SS model, the design of the control system and the assessment of the system performance are carried out. Important systems characteristics are captured by the model, i.e. attenuation levels, frequency response and control voltage levels. This reveals that the proposed FE can be used to model and assess structural behaviour in a relatively simple and efficient way.

A new magnetorheological (MR) mount consisting of an MR fluid encapsulated in a polymeric solid is presented. The mechanical properties of the proposed mount are controllable through an externally applied magnetic field. The dynamic behavior of this system under various magnetic fields has been investigated by means of oscillatory compression cycles over a frequency range of 0.1–10 Hz for various deformations (less than 1 mm). The energy dissipation in the material is analyzed as related to strain amplitude, strain frequency and magnetic field strength. The field induced damping mechanism is discussed in terms of the damping exponent. A phenomenological model is presented to account for the dynamic behavior of the MR fluid–elastomer mount's vibration isolators under oscillatory compressive deformations. This model is a two-element system comprised of a variable friction damper and a nonlinear spring. The parameters of the model have been identified by a series of harmonic loading tests. The theoretical and experimental results are in excellent agreement. Both experimental and theoretical results have demonstrated that the proposed MR fluid–elastomer mounts show promise in applications where tuning vibration characteristics of a system are desired, such as altering natural frequencies, mode shapes, and damping properties.

Modal filters may be obtained by a properly designed weighted sum of the output signals of an array of sensors distributed on the host structure. Although several research groups have been interested in techniques for designing and implementing modal filters based on a given array of sensors, the effect of the array topology on the effectiveness of the modal filter has received much less attention. In particular, it is known that some parameters, such as size, shape and location of a sensor, are very important in determining the observability of a vibration mode. Hence, this paper presents a methodology for the topological optimization of an array of sensors in order to maximize the effectiveness of a set of selected modal filters. This is done using a genetic algorithm optimization technique for the selection of 12 piezoceramic sensors from an array of 36 piezoceramic sensors regularly distributed on an aluminum plate, which maximize the filtering performance, over a given frequency range, of a set of modal filters, each one aiming to isolate one of the first vibration modes. The vectors of the weighting coefficients for each modal filter are evaluated using QR decomposition of the complex frequency response function matrix. Results show that the array topology is not very important for lower frequencies but it greatly affects the filter effectiveness for higher frequencies. Therefore, it is possible to improve the effectiveness and frequency range of a set of modal filters by optimizing the topology of an array of sensors. Indeed, using 12 properly located piezoceramic sensors bonded on an aluminum plate it is shown that the frequency range of a set of modal filters may be enlarged by 25–50%.

The aim of this work was to develop a methodology for the characterization of complex piezocomposites under external mechanical forces. In this specific procedure the samples were axially loaded in a universal mechanical test machine and monitored with an electrometer. The force versus displacement and the generated charge versus the applied force were measured. Cymbal piezocomposites were chosen due to their complex design which illustrated the effectiveness of the proposed methodology during the application of compression force loops.

The occurrence of depolarization can be evaluated by measuring the electrical charge generated during the application of a compression loop. The results showed the dependence of electromechanical properties on both the PZT ceramics and the cymbal piezocomposite with the compressive load loops. The depolarization effect associated with the mechanical stress induced by switching of a non- 180° ferroelectric domain was evaluated.

This paper addresses the development of superstructure fiber Bragg gratings (FBGs) by laser-assisted direct writing of on-fiber metallic films. A novel laser direct write method is characterized to fabricate periodic films of silver nanoparticles on the non-planar surface of as-fabricated FBGs. Silver films with a thickness of 9 µm are fabricated around a Bragg grating optical fiber. The performance of the superstructure FBG is studied by applying temperature and tensile stress on the fiber. An opto-mechanical model is also developed to predict the optical response of the synthesized superstructure FBG under thermal and structural loadings. The results show that the reflectivity of sidebands in the reflection spectrum can be tuned up to 20% and 37% under thermal and structural loadings, respectively. In addition, the developed superstructure FBG is used for simultaneous measurement of force and temperature to eliminate the inherent limitation of regular FBGs in multi-parameter sensing.

This paper presents an experimental investigation on vibration control using an active mount activated by piezostack actuators. After describing the schematic configuration and operational principle of the proposed active mount, dynamic characteristics of the rubber element and the piezostack are experimentally identified. An active mount is then manufactured using a rubber element and two piezostack elements. Prior to validating vibration control of the proposed active mount, fundamental characteristics such as resonant frequency, deflection at rated load, strength, shock and fatigue characteristics are experimentally investigated. A two-degree-of-freedom control system in which an active mount is installed with a supported mass of 100 kg is established for evaluating vibration control performance. In order to actively attenuate the vibration transmitted from the base excitation (50–1000 Hz), a negative velocity feedback controller is experimentally realized. Control responses such as mass acceleration are evaluated in both frequency and time domains.

One of the first 1D constitutive equations for shape memory alloys (SMA) was presented by Brinson; it became the basis for later works, typically. In Brinson's equation, several proposed functions are considered in order to simplify the model and obtain the constitutive equation for SMA. In a recent paper, Buravalla and Khandelwal have shown certain anomalies in Brinson's model and have tried to present a modified model which unlike Brinson's model satisfies the compatibility condition. However, their formulation, besides being lengthy, lacks clarity and in particular does not address proper expressions for transformation tensors. In the present work, Brinson's constitutive equation is derived from fundamental relations using a simple, clear-cut and straightforward approach. Without any extra and unnecessary assumption the modified transformation tensors are derived from original definitions. The new expressions are compared with those of Brinson and the consistency of the model is confirmed.