Siak Piang Lim

Hybrid energy harvester based on piezoelectric and electromagnetic mechanisms

A novel hybrid energy harvester integrated with piezoelectric and electromagnetic energy harvesting mechanisms is investigated. It contains a piezoelectric cantilever of multilayer piezoelectric transducer (PZT) ceramics, permanent magnets, and substrate of two-layer coils. The effect of the relative position of coils and magnets on the PZT cantilever end and the poling direction of magnets on the output voltage of the energy harvester is explored. When the poling direction of magnets is normal to the coils plane, the coils yield the maximum output voltage, i.e., the type I and III devices. The maximum output voltage and power from the PZT cantilever of the type III device are 0.84 V and 176 µW under the vibrations of 2.5-g acceleration at 310 Hz, respectively. And the maximum output voltage and power from the coils are 0.78 mV and 0.19 µW under the same conditions, respectively. The power density from the type III device is derived as 790 µW/cm3 from piezoelectric components and 0.85 µW/cm3 from electromagnetic elements.

A MEMS rotary comb mechanism for harvesting the kinetic energy of planar vibrations

A capacitive energy harvester based on in-plane rotary combs is proposed and studied. It is capable of collecting kinetic energy from planar ambient vibrations for low frequency operation. The design and simulation of capacitance among rotary combs, ladder spring and resonant frequency of the whole rotary comb energy harvester are presented in this paper. This device is fabricated in SOI (silicon-on-insulator) wafers by deep silicon etching technology. The dimensions of the prototype are about 7.5 mm × 7.5 mm × 0.7 mm. A maximum measured output power in air for vibrations of 0.5 g, 1 g, 1.5 g, 2 g and 2.5 g is 0.11 µW, 0.17 µW, 0.24 µW, 0.3 µW and 0.35 µW, respectively, when the loading resistance matches the parasitic resistance of 80 MΩ at the resonant frequency of 110 Hz. In order to reduce the air damping effect, the prototype is packaged by having a metal cap to form the vacuum level of 3 Torr. The testing results in vacuum level of 3 Torr show that the resonant frequency decreases from 110 Hz in air to 63 Hz, and the maximum electrical output power at 0.25 g is 0.39 µW.

A LBM-DLM/FD method for 3D fluid-structure interactions

The previously developed LBM-DLM/FD method derived from the lattice Boltzmann method and the distributed Lagrange multiplier/fictitious domain method is extended to deal with 3D fluid-structure interactions. In our current algorithm, the fluid motion is solved by LBM, the deformation of the solid body is solved by the finite element method, and the Lagrange multiplier is solved on the low-order mesh. Three numerical examples are employed to validate the LBM-DLM/FD method and reveal the potential of the method to deal with the fluid/elastic-body interaction problems.

Solving traveling salesman problems by genetic algorithms

Abstract The gene section ordering on solving traveling salesman problems is analyzed by numerical experiments. Some improved crossover operations are presented. Several combinations of genetic operations are examined and the functions of these operations are analyzed. The essentiality of the ordering of the gene section and the significance of the evolutionary inversion operation are discussed. Some results and conclusions are obtained and given, which provide useful information for the implementation of the genetic operations for solving the traveling salesman problem.

Successive approximation training algorithm for feedforward neural networks

Abstract A novel algorithm based on successive approximation training for feedforward neural networks is presented in this paper. The convergence of the algorithm is analysed theoretically and the training error is estimated. Theoretical analysis shows that the novel training algorithm is able to overcome the stalemate problem in the later training stage of the traditional algorithms. Numerical experiments show that the proposed algorithm increases the rate of convergence and improves the generalization performance by avoiding local minima.

A computational fluid dynamics study on geometrical influence of the aorta on haemodynamics

OBJECTIVES Cardiovascular diseases, such as atherosclerosis and aneurysm, are closely associated with haemodynamic factors that are governed by luminal geometry. The present work aimed to study the effect of geometrical variation of aging aortas on haemodynamics. METHODS Six aged subjects with intricate geometrical features, such as bulging or twisted supra-aortic arteries, sharply curved arch and double-curved descending aorta, were chosen from our medical database. These six geometrically variant aortas were reconstructed and the pulsatile nature of the blood flow of these subject-specific aorta models investigated using computational fluid dynamics simulations. Realistic time-dependent boundary conditions are prescribed for various arteries of the aorta models. RESULTS This study suggests that haemodynamics in the human aorta is highly dependent on geometrical features. The positioning and contouring of the supra-aortic arteries may be associated with the skewness of velocity profiles. The flow profiles in the aortic arch or bends are generally skewed towards the inner curvature wall and this skewness may give rise to the formation of secondary flow in the inner curvature wall of the distal arch. The degree of vorticity in the distal aortic arch is found to be related to the arch curvature. The helical nature of aortic haemodynamics is predominant in the systole phrase when it begins with a left-handed rotation and then vanishes in the ascending aorta, whereas a right-handed rotation persists in the distal aortic arch. Lower wall shear stress is also found in the ascending regions where secondary flow is present. CONCLUSIONS The aorta with an irregular contour and large degree of curvature at its arch favours the development of the intra-aortic secondary flow that subsequently relates to the pathogenesis of atheroma. The present study identifies the general trend of haemodynamic behaviours associated with various local geometrical features. Combining the knowledge of the correlation between haemodynamics and the underlying risks in the development of cardiovascular diseases, our study hopes to provide a better understanding of the relationship between aortic morphology and developing pathobiology of cardiovascular diseases. As such, early medical planning as well as surgical interventions can be designed to retard or prevent the development of cardiovascular diseases.

A kinematic analysis of cylindrical ultrasonic micromotors

Abstract The present work deals with a theoretical analysis of operating principle of cylindrical ultrasonic micromotors. Although the movement has been realised by experiments and measurements, a fairly deep-going mathematical description on the motion has not been seen in literature. The work carried out in this paper is based on simplified beam bending vibration model. The obtained expressions provide a theoretical understanding of the motor operation and driving mechanism. The analysis is also valuable for further modelling and simulation of the motors.

Development and numerical characterization of a new standing wave ultrasonic motor operating in the 30-40kHz frequency range.

The purpose of this research is to present a new design of standing-wave ultrasonic motor. This motor uses three piezoelectric actuating blocks which deform appropriately when powered up. The deformations of the blocks in ultrasonic range are internally amplified via the design of the motor by about 80 times and collectively yield an elliptical trajectory for the driving head of the motor. Finite Element Analysis using ANSYS was performed for both dynamic analysis and optimization of a prototype motor. The numerical results verified that at steady state, the motor can achieve vibrations in micro-meter level and the velocity can reach decimeter scale, satisfying the fast speed requirement as a positioning actuator.

Development and validation of two subject-specific finite element models of human head against three cadaveric experiments

Head injury, being one of the main causes of death or permanent disability, continues to remain a major health problem with significant socioeconomic costs. Numerical simulations using the FEM offer a cost-effective method and alternative to experimental methods in the biomechanical studies of head injury. The present study aimed to develop two realistic subject-specific FEMs of the human head with detailed anatomical features from medical images (Model 1: without soft tissue and Model 2: with soft tissue and differentiation of white and gray matters) and to validate them against the intracranial pressure (ICP) and relative intracranial motion data of the three cadaver experimental tests. In general, both the simulated results were in reasonably good agreement with the experimental measured ICP and relative displacements, despite slight discrepancy in a few neutral density targets markers. Sensitivity analysis showed some variations in the brains relative motion to the material properties or markers location. The addition of soft tissue in Model 2 helped to damp out the oscillations of the model response. It was also found that, despite the fundamental anatomical differences between the two models, there existed little evident differences in the predicted ICP and relative displacements of the two models. This indicated that the advancements on the details of the extracranial features would not improve the models predicting capabilities of brain injury.

Effects of interface slip and viscoelasticity on the dynamic response of droplet quartz crystal microbalances.

In the present paper we first present a derivation based on the time-dependent perturbation theory to develop the dynamical equations which can be applied to model the response of a droplet quartz crystal microbalance (QCM) in contact with a single viscoelastic media. Moreover, the no-slip boundary condition across the device-viscoelastic media interface has been relaxed in the present model by using the Ellis-Hayward slip length approach. The model is then used to illustrate the characteristic changes in the frequency and attenuation of the QCM with and without the boundary slippage due to the changes in viscoelasticity as the coated media varies from Newtonian liquid to solid. To complement the theory, experiments have been conducted with microliter droplets of aqueous glycerol solutions and silicone oils with a viscosity in the range of 50 approximately 10,000 cS. The results have confirmed the Newtonian characteristics of the glycerol solutions. In contrast, the acoustic properties of the silicones oils as reflected in the impedance analysis are different from the glycerol solutions. More importantly, it was found that for the silicone oils the frequency steadily increased for several hours and even exceeded the initial value of the unloaded crystal as reflected in the positive frequency shift. Collaborative effects of interfacial slippage and viscoelasticity have been introduced to qualitatively interpret the measured frequency up-shifts for the silicone oils. The present work shows the potential importance of the combined effects of viscoelasticity and interfacial slippage when using the droplet QCM to investigate the rheological behavior of more complex fluids.