Journal of Intelligent Material Systems and Structures

Semi-passive damping techniques have been developed recently to address the problem of structural damping. Contrary to the standard passive piezoelectric damping, these new techniques adapt to environmental variations. Moreover, they present interesting multimodal damping performances. However, their efficiency is strongly correlated with their electromechanical coupling. The enhanced semi-passive damping technique presented herein compensates for this drawback. It reinforces the electromechanical coupling by artificially increasing the voltage amplitude delivered by the piezoelectric patches. Theoretical predictions and experimental results show a −24 dB attenuation on the vibration of a resonant cantilever steel beam, while reducing the piezoelectric material volume by 83%.

This article describes the active vibration control of a plate using a self-sensing actuator (SSA) and an adaptive control method. In a self-sensing actuator, the same piezoelectric element functions as both a sensor and an actuator so that the total number of piezoelectric elements required can be reduced. A method to balance the bridge circuit of the SSA was proposed and its effectiveness was confirmed by using an extra piezoelectric sensor, which is not necessary for balancing bridge circuits of SSA in future applications. A control system including the SSA and an adaptive controller using a finite impulse response (FIR) filter and the filtered-X LMS algorithm was established. The experimental results show that the bridge circuit was well balanced and the vibration of the plate was successfully reduced at multiple resonance frequencies below 1.2 kHz.

In this article, an identification technique for detecting delaminations in composite laminates is proposed, which uses the distributed piezoelectric actuators/sensors and the conception of transfer function. In this technique, the configuration of arrays of actuators/sensors is carefully designed to enhance the efficiency of the identification algorithm based on the transfer function. A beam example is employed to study the characteristics and effectiveness of the present identification approach, numerically. The experimental data are simulated from a FEM technique of higher-order plate theory for adaptive composite laminates, which is extended for delaminated laminates by implementing the displacement continuity conditions at the delamination front.

This article presents the noise reduction performance of piezoelectric smart panels featuring piezoelectric shunt damping. A piezoelectric smart panel is a plate structure on which a piezoelectric patch with an electrical shunt circuit is attached. When an incidence sound is impinged on the panel structure, the structure vibrates and the attached piezoelectric patch produces electrical energy, which is effectively dissipated as heat via an electrical shunt circuit. Since the energy dissipation strongly depends on the vibration mode of the panel structure, many patches are required for multiple vibration modes. Instead of using multiple piezoelectric patches, a single piezoelectric patch is used in conjunction with blocked shunt circuit for multimode shunt damping. Modeling, shunt parameter tuning, and implementation of the blocked shunt circuit on the panels are explained.

A new type of large-displacement actuator called RAINBOW (Reduced And Internally Biased Oxide Wafer) has been fabricated by the chemical reduction of PSZT antiferroelectric ceramics and its properties are investigated. It is found that PSZT is easily reduced and the optimal conditions for producing RAINBOW samples were determined to be 870°C for 2-3 h. The AFE-FE phase transitions occur at a lower field strength in the RAINBOW actuators compared with normal PSZT actuators. Larger axial displacement (about 190 mm) have also been obtained from the RAINBOW actuators by application of electric fields exceeding the phase switching level. However, the field-induced displacement of the RAINBOW actuator is dependent on the manner of application of load on the samples.

This study describes a method for analyzing the F-T characteristics of the thickness modes of a doubly rotated Y-cut anisotropic quartz crystal, including a-, b-, and c-modes by using the Christoffel equation that describes sound waves in solids. With this method, the F-T characteristics of the independent rotational angles 3/1 can be predicted. Based on the predicted F-T characteristic curve, the potential application of some cut-types as sensors is discussed. Combined with other methods, such as crystal force-frequency characteristic analysis, this method is expected to provide a research platform for studying new cut-types for various applications, such as frequency control and physical, chemical, and biological sensors, etc.

A health monitoring system was designed and installed on Dafosi Bridge, the largest cable-stayed bridge across the Yangtze River in western China. This article briefly describes an online deflection monitoring system, the most important sensing subsystem of the health monitoring system. It can be divided into two major components, one for measurement, and one for control and data processing. The measurement system itself includes two types of deflection sensors to monitor the lateral displacement of the two towers and the flexural and torsional displacement of the main girder. Sensor outputs are pre-processed locally and sent to the host computer at the management center via the Internet. The system design and implementation are reviewed, and the results of data from two kinds of sensors are presented.

A soft actuator with a giant bending motion controlled by hydrogen pressure for artificial muscles has been innovated. It resembles a bimetal and is constructed with soft silicone rubber sheets for driving and supporting. The LaNi₅ hydrogen storage alloy powder is dispersed in the driving sheet. The reversible motion is observed and operated by hydrogenation and degassing. The giant bending motion of over 4000 ppm of strain was observed from 2 min to 3 h of hydrogenation time. The actuator developed shows a giant bending motion as large as that of a typical shape memory alloy.

An automatic defect testing system is dealt with in this article. It includes two parts, defect feature extraction, and defect classification and sizing. Defect feature extraction is carried out by adaptive filter deconvolution. The time delay between two consecutive taps of the adaptive filter is one half cycle of the ultrasonic echo to be processed. Wideband ultrasonic defect echoes of center frequency 1.2 MHz generally have 2-4 cycles and 100-200 data points for a 50 MHz sampling rate. After deconvolution, data are reduced to 4-8 points, and the frequency bandwidth is greatly extended. As a result, the defect features stand out. The deconvolved defect echoes are presented to an artificial neural network (ANN) for automatic defect classification and sizing. Two application examples are given in this article, exact classification and reasonable sizing accuracy have been achieved.

The Hilbert-Huang Transform (HHT) approach is used for signal processing to discover the possible damages existing in a structure. A program is written in Fortran and in Matlab, and then verified by two simple cases with known solutions. The HHT method is then utilized to analyze the actual benchmark data of UBC (University of British Columbia) for the purposes of structural health monitoring. The results demonstrate that HHT method has the capability of: (a) recovering the actual signals’ time-frequency feature; (b) detecting and locating the actual structural damages; (c) detecting the instant of the impact load or of the damage taking place in active structural health monitoring. The method of Empirical Mode Decomposition (EMD) is used to eliminate noise. Results show that EMD method is better than the Wavelet method for the de-noising purpose.

A new type of micro swimming mechanism is examined for the development of medical microrobots working in human blood vessels. The magnetic micro swimming mechanism without the wire for supplying the energy is driven by the alternating magnetic field. The magnetic swimming mechanism is examined in a transparent polyvinylchloride pipe filled with a viscous liquid. The test fluid used in the experiment is glycerin. The Helmholtz coil and a bipolar power supply are used to apply the alternating magnetic field in the experiment. Locomotive characteristics of the swimming mechanism in a viscous liquid are analyzed by a high-speed video camera system. The dynamic behavior of a micro swimming robot in a viscous liquid is revealed.

Hairy adhesive pads are used by many animals and insects which can move on the ceilings and walls, such as gecko, spider, fly and some beetles. The effects of material properties and contact geometry were experimentally studied. The softest material has the highest adhesion and the surface roughness has hardly any effects on adhesion. The contact geometry and surface roughness influence adhesion heavily. The adhesion increases with the increase of normal force for a flat-to-flat contact, but does not get affected for a spherical sapphire ball to flat polyurethane contact. The adhesion is not affected by contact angles for soft connections, but heavily decreases for hard connections. The results are important data for bionic hairy foot design.

This article describes the results of some experiments concerning wing morphology and flight performance of some flying insects: cicadas, dragonflies, and gadflies. First, the wing structures of these insects are measured down to the minutest detail by a three-dimensional curve-shaped measuring system. The surface shapes of the insect wings are mapped by distinct three-dimensional images. From the three-dimensional images, correlation coefficients are calculated by comparisons of the distribution of undulation on the wings. The surface shapes and the correlation coefficients show a difference in functions for flapping flight between each wing. Second, the distribution of velocity fields around a flapping cicada and a flapping dragonfly are visualized with a PIV system to identify the airflow generated by the wings. The distribution of velocity vectors for one stroke of a dragonfly wing is explained in the article. Additionally, the difference of airflow around the wings of a dragonfly and a cicada are revealed. It is found that the flapping forewing of the dragonfly carries out an important motion in its highly efficient flight.

Shape memory polymers (SMPs) have attracted great interest in recent years. The SMP foams are outstanding, owing to their high shape recovery ratio in compression. They can be used for, for instance, micro foldable vehicles, shape determination, and microtags. This article presents a study on the thermomechanical behavior of a polyurethane SMP foam, associated with these three applications. This includes four types of tests namely, compression test, free recovery test, constrained cooling test, and gripping test.

In order to explain the misting-free treatment by sheet electron beam irradiation (SEBI) for sapphire lens setting on endoscope top, influences of SEBI on surface energy are investigated. The SEBI increases surface energy, resulting in force-distance curve used for atomic force microscope. Based on the results of X-ray photoelectron spectroscopy, the SEBI enhances the bonding rates of -C-O- and -C-O-O- and decreases -C-C- bonding rate. On the other hand, influences of SEBI on surface water wettability are investigated. The SEBI enhances the wettability of the sapphire surface for water, n-hexadecan, and 1-bromonaphthalene. Since the adhesion molecular change coincides with the surface energy change, the dipole of adhesion molecular is the dominant factor to control the surface energy. In order to explain to the dipole factor change, the electron charge is measured, too. From the results, the surface energy change can be explained by the adhesion molecular change and electron charging.

In this article, the experimental modeling and active shape control of hybrid composite structures actuated by shape memory alloy (SMA) wires are presented and discussed. The thermomechanical properties of the SMA wires are experimentally measured. SMA actuators with residual strains are prepared by loading-unloading tensile tests. Hybrid composite structures are established by attaching the SMA actuators on the surface of a graphite/epoxy composite beam and plate by bolt-joint connectors. The first-order numerical model is used to model the response of the hybrid composite structures attached to the SMA actuators. The parameters of the first-order model are experimentally determined and the response is compared with experimental data. For faster and more accurate shape/deflection control of the hybrid composite structure, feedforward and proportional integral derivative (PID) feedback controllers are designed and applied to the hybrid composite structure. The PID feedback controller significantly improves the performance of the SMA actuators.

This article presents the development of an implanted artificial urethral valve that is used for the treatment of urinary incontinence, with emphasis on a transcutaneous power transmission system with closed-loop thermal control function. The valve uses a shape memory alloy (SMA) plate as the actuator, which is activated with batteries placed outside a patient’s body using a transcutaneous power transmission system. The power transmission system is equipped with an implanted temperature monitor circuit and a temperature controller to prevent the SMA actuator from being overheated during a prolonged urination. Laboratory experiments and animal experiments, both in vitro and in vivo, show that the developed power transmission system can successfully control the temperature of the SMA actuator to activate the valve without excessive heating of the SMA actuator.

An optical fiber sensor based on surface plasmon resonance (SPR) phenomenon that can be used for liquid refractive index testing is presented in this article. The effect of various parameters like the refractive index of the core and the liquid type on the shape of the SPR spectrum is analyzed, utilizing relative spectrum measurement technology. The relationship curves between several kinds of liquids with the same refractive index with their resonance wavelengths are also obtained using the sensing probe. Furthermore, experimental results of liquids with high refractive index reveal that the improved probe with SiO film has the ability to extend the detection upper limit of refractive index and keep the toughness of optical fiber at the same time.

In order to greatly reduce the sedimentation in magnetorheological fluids (MRF), which will result in variable-time dynamic behaviors of MRF based vibration-damping devices, a kind of magnetorheological grease (MRG), whose rheological property can also be significantly changed on the application of an external magnetic field, is presented, and a MRG based disk-type damper in shear operation for rotational machinery is developed. This article reports the experimental results about the controllability of the disk-type MRG damper on the dynamic behavior of a rotor system, the effectiveness of the disk-type MRG damper for attenuating the rotor’s vibration, and the suitability of the MRG damper for a feedback vibration control of rotor systems in a flexible rotor. It is shown that the dynamic behavior of the disk-type MRG damper can be controlled on the application of an external magnetic field produced by a low voltage electromagnetic coil. The disk-type MRG damper can significantly change the dynamic characteristics of a rotor system, and is suitable for an actuator to actively control the vibration of rotor systems.

A magnetorheological (MR) damper model is established and linearized based on theory analyses and real testing. Since the mathematical model of the suspension system is nonlinear and complicated, a model-free fuzzy control algorithm is employed to design a controller for achieving vibration isolation. As a pilot study, two MR dampers are used to replace the passive ones of the front half-car. A quarter-car fuzzy intelligent controller is employed to control the two MR independent suspension systems, respectively. The performance of the MR suspension system is evaluated by road testing. The test results indicate that the vibration of the vehicle body and unsprung mass are both reduced significantly.

A prototype of an exercising bicycle with a key part of concentric cylinders has been designed and characterized employing electrorheological (ER) fluids based on zeolite and silicone oil. The radius and width of the cylinders have been optimized so that there is minimum power consumption from the high voltage power source. The performance of the prototype has been experimentally determined. Experimental results show that the resistance increases significantly with the increase of applied electric field and the power consumption of the exercising bicycle is <0.5 W. The research shows the advantages of using ER fluids in this kind of an apparatus.

The research on magnetorheological (MR) damping technology is booming in recent years. Especially on application to vehicles, both good ride comfort and steering stability must be taken into account. Accordingly, high scalability of MR dampers and their magnetic design are of significance. In this article, the magnetic design of an MR damper is proposed, and a finite element (FE) analysis on the magnetic saturation is discussed for the utmost improvement of the high force. Through experimental verification, the damper force is effectively scaled by the magnetic design.

The effect of microscale contact of rough surfaces on adhesion and friction under negative normal forces is experimentally investigated. The adhesion do not vary with the normal forces on the condition of single point contact - sapphire ball to flat polyurethane (PU). The adhesion increased with the normal forces according to logarithmic relation in the circumstances of rough surface contact, which was assumed as a great number of point contacts. Under negative normal forces - adhesion, the tangential forces increased with the decrease of negative normal forces linearly. The results reveal why a gecko’s toe must slide slightly on the target surface when it contacted the ceiling and suggest how the biomimetic gecko foot is designed.

This study deals with the development of a simple and multifunctional piezoelectric transducer, which can detect two or more species at one time. The transducer for testing consists of an aluminum cantilever beam and a piezoceramic patch. A piezoelectric impedance-based measurement technique is proposed for detecting a very small biospecies mass sensitively. Furthermore, two different types of biomembranes are coated on the beam so that they can detect two kinds of species without causing interference with each other. The problem as to how to determine the optimal positions for coating the membranes are investigated in detail by the finite element method (FEM). The numerical simulations showed a good agreement with the experimental results. Further, a concept for the design of a multifunctional transducer is proposed based on the mode function, and its validation is proved experimentally.

This article describes a new approach to harvest electrical energy from a mechanically excited structure equipped with piezoelectric elements. Standard harvesting circuits using piezoelectric elements as an electric generator consist of an AC-DC converter coupled to a load. The technique proposed herein is fully compatible with the standard approach. The difference consists in adding up an electrical switching device connected in parallel with the piezoelectric elements. The switch device is triggered on the maxima or minima of the displacement and realizes a voltage inversion through an inductor. This method allows the artificial increase of the piezoelements’ output voltage, resulting in a significant increase of the electrical power flow. It is shown that the power flow transfer strongly depends on the structure electromechanical coupling coefficient. For a weakly coupled structure using this new technique, the electrical power can be increased by over 400%.