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Transparent object detection and reconstruction are significant, due to their practical applications. The appearance and characteristics of light in these objects make reconstruction methods tailored for Lambertian surfaces fail disgracefully. In this paper, we introduce a fixed multi-viewpoint approach to ascertain the shape of transparent objects, thereby avoiding the rotation or movement of the object during imaging. In addition, a simple and cost-effective experimental setup is presented, which employs two single-pixel detectors and a digital micromirror device, for imaging transparent objects by projecting binary patterns. In the system setup, a dark framework is implemented around the object, to create shades at the boundaries of the object. By triangulating the light path from the object, the surface shape is recovered, neither considering the reflections nor the number of refractions. It can, therefore, handle transparent objects with a relatively complex shape with the unknown refractive index. The implementation of compressive sensing in this technique further simplifies the acquisition process, by reducing the number of measurements. The experimental results show that 2D images obtained from the single-pixel detectors are better in quality with a resolution of 32&times, 32. Additionally, the obtained disparity and error map indicate the feasibility and accuracy of the proposed method. This work provides a new insight into 3D transparent object detection and reconstruction, based on single-pixel imaging at an affordable cost, with the implementation of a few numbers of detectors.

In this paper, we present a novel low-power UV sensor instrumentation based on ZnO thin-film and langasite crystal microbalance (LCM) composite resonator. The design of this sensor utilizes the exceptional transient response characteristics of thickness shear mode langasite crystal and UV sensitivity of annealed ZnO thin film. Our comparative transient analysis of langasite and quartz crystals shows that langasite crystal has high stability and fast relaxation times, and requires a fraction of excitation power in comparison to that of quartz. Upon investigating the equivalent circuit components, we discovered that high value of motional capacitance of LCM resulted in these contrasting transient responses in LCM and QCM. This high motional capacitance can be further attributed to the high electromechanical coupling coefficient ( K 2 ) of piezoelectric langasite crystal. Motivated by these observed characteristics, we proposed a novel sensor instrumentation that is simple yet effective in simultaneous measurements of the frequency, dissipation factor, and the amplitude of oscillation of a LCM. Moreover, our measurements allow for direct monitoring of any change in piezoelectricity of ZnO thin film. Our new measurement approach uses a one-shot pulse instead of conventional sinusoidal waveform to drive the crystal, which allows for simple instrumentation and requires very low input power. The transient response of the crystal shows that the crystal oscillates at its fundamental frequency and the amplitude of oscillation decays exponentially. From the recorded decay curve, the frequency of the freely oscillating crystal, and other important crystal parameters were calculated. We have utilized this mechanism to demonstrate highly sensitive ZnO thin film and LCM based UV sensor. Highest sensitivity of 35.8 ppm per μW/cm 2 was observed for the LCM coated with 400 nm ZnO film. Additionally, the influence of UV on the piezoelectric output of ZnO thin film was also characterized by monitoring the DC offset of the output oscillations. Our findings in this work opens scope for developing low-power acoustic sensors with significant implications towards self-powering sensors.

This paper investigates the propagation of guided ultrasonic wave in pipes with bends using finite element simulation. The defect detectability in pipes with bends, using time delay focusing and synthetic focusing by common source method (CSM) are studied. Results show that the time delay focusing technique improves the confidence in detecting a small defect (3.8% cross-sectional area) beyond the bend, but it is unable to detect defects close to other features like welds or bends. Meanwhile, CSM is able to improve defect detection beyond and close to welding and bends. However, a reference image of a defect-free pipe is needed to detect defects near welds.

Well-aligned (c-axis oriented) ZnO nanowire arrays were successfully synthesized on Si (1 0 0) substrates through an optimized self-seeding thermal evaporation method. An open-ended chemical vapor deposition (CVD) setup was used in the experiment, with argon and purified air as reaction gases. Epitaxial growth of c-axis oriented ZnO nanowires was observed for 5 sccm flow rate of purified air, whereas Zn/Zn suboxide layers and multiple polycrystalline layers of ZnO were obtained for absence and excess of purified air, respectively. Ultraviolet (UV) sensing and emission properties of the as-grown ZnO nanostructures were investigated through the current–voltage (I–V) characteristics of the nanowires under UV (λ = 365 nm) illumination of 8 mW/cm2 and using photoluminescence spectra. Nanowires grown under optimum flow of air emitted four times higher intensity of 380 nm UV light as well as exhibited 34 times higher UV radiation sensitivity compared to that of other nanostructures synthesized in this study.

An ultraviolet (UV) sensor consisting of a langasite (La3Ga5SiO14) thickness shear mode resonator and ZnO nanostructure sensing medium was fabricated. For the first time, ZnO nanostructures, including nanorods, polycrystalline film, and well-aligned nanowires, were grown directly on the active area of langasite crystal microbalance (LCM) by the thermal evaporation method without the aid of any transfer technique. As a key part of the growth process, zinc vapor trapping and two-stage temperature ramping were employed to achieve catalyst-free, self-seeding growth of ZnO nanowires at growth temperatures below 600 °C. Under illumination of 365-nm UV light, a downshift in resonant frequency was observed for the LCMs due to acousto-electric interaction between photo-induced carriers and the shear waves. ZnO nanowires showed enhanced UV photosensitivity compared with that of nanorods or polycrystalline film. LCM with nanowires exhibited maximum shift of 157.5 Hz for several ON–OFF UV cycles and generated photocurrent of 235 $\mu \text{A}$ for 5 V bias. Nanowire-based sensor also demonstrated excellent response and recovery times of 11 and 43 s, respectively. All the ZnO nanostructure-coated LCMs showed good stability and repeatability in UV sensing.

In this paper, several approaches are applied for 3D reconstruction of range gated imaging with the objective to improve the 3D performance in terms of accuracy and resolution. Feasibility of the proposed image processing, 3D reconstruction model, super-resolution technique, and mesh refinement is demonstrated. Our test case shows that the depth error of 3D reconstruction is improved from 2.26% to 1.65% after mesh refinement. This gives a constructive idea to provide optimised 3D solution and benefit various applications. The proposed approaches and the findings presented may stimulate further interest in the relevant fields such as machine vision and 3D active imaging.

Nanofluid exhibits great potential in enhancing thermal performance of cooling devices. From the second-law point of view, we investigate the entropy generation of nanofluid flow in asymmetrically heated porous microchannels with solid-phase heat generation. Based on two-energy-equation model, the closed-form temperature distributions of porous medium solid phase and nanofluid are obtained. The thermal non-equilibrium entropy generation function is derived by using differential method. The results show that the thermal asymmetries significantly affect the temperature distribution and hence the heat transfer irreversibility in the system. However, the fluid friction irreversibility is barely affected by the thermal asymmetries. For the case without solid-phase heat generation, the entropy generation can be minimized when the wall heat flux ratio is 1/2. Besides, there is an optimum Reynolds number at Re=22 which further reduces the entropy generation. For the case with solid-phase heat generation, the entropy generation is minimized at wall heat flux ratio of 3/4, but the optimum Reynolds number vanishes. The solid-phase heat generation irreversibility dominates other irreversibilities and intensifies the entropy generation conspicuously. The second-law performance of nanofluid can be enhanced only when the internal heat generation is relatively low. When the suspended nanoparticle is smaller than the threshold size, the entropy generation can be reduced as much as 42%. The intensification of solid-phase heat generation significantly reduces the discrepancy between the thermal equilibrium and non-equilibrium models to less than 1%. This signifies the importance of considering thermal asymmetries and internal heat generation in the performance characterization of nanofluid flow in porous media.

Under thermally non-equilibrium condition, the thermal performance of water–alumina nanofluid convection in asymmetrically heated porous media with internal heat generation is investigated analytically. The effects of thermal asymmetry, nanoparticle size and solid-phase heat generation on the thermal characteristics of nanofluid flow in porous microchannels are elucidated. Due to the effect of viscous dissipation, the heat flux at the channel wall is reversed, leading to the phenomenon of heat flux bifurcation when nanoparticle size increases. On the other hand, the solid-phase heat generation in porous medium induces the heat flux bifurcation at smaller nanoparticle size. The heat transfer enhancement of nanofluid is the largest for the case of symmetrical heating, with an increase of average heat transfer coefficient of 47% compared to that of the case of asymmetrical heating. In the presence of solid-phase heat generation, the heat transfer enhancement of nanofluid occurs over a larger range of Reynolds number. When the solid-phase heat generation is significant, a pronounced error can be induced in the simplified thermal equilibrium model.

Based on the first-law and second-law of thermodynamics, we investigate thermal performance and entropy generation of water–alumina nanofluid flows in porous media embedded in a microchannel under local thermal non-equilibrium condition. Analytical closed-form solutions of two-dimensional temperature distributions are obtained for the cases with and without the viscous dissipation term in the energy equation. The thermal non-equilibrium entropy generation function is derived using the differential method. Due to the embedment of the porous medium in the microchannel and the suspension of the nanoparticle in the working fluid, the viscous dissipation effect is magnified significantly, altering thermal characteristics and entropy generation of the system. For the case where the viscous dissipation effect is neglected, total entropy generation and fluid friction irreversibility are overrated while heat transfer irreversibility is remarkably underestimated. In a low-aspect-ratio microchannel, the suspension of nanoparticles in the fluid decreases the thermodynamic efficiency from the second-law point of view. Utilization of nanofluids in a high-aspect-ratio microchannel enhances exergetic effectiveness in low-Reynolds-number flow regime. By reducing the nanoparticle size, entropy generation can be decreased by as much as 73%. The optimum Reynolds number associated with minimum entropy generation for nanofluid flow in a porous microchannel is identified. The optimum range of porous medium permeability is characterized by Da ⩾ 10 - 1 . It is observed that effectiveness of the interstitial heat transfer between the solid and fluid phases of the porous medium induces a pronounced effect on the entropy generation, signifying the importance to consider the thermal non-equilibrium condition in the second-law performance analysis of porous-medium flow.

Despite the advances made in laser and sensor technology, setting up an accurate range gated imaging system remains a challenge. In this paper, we emphasise on the importance of system setup and its impacts to the performance of three-dimensional (3D) range gated reconstruction. Study is performed to analyse some of the system setup criteria and parameters involved in the laser and camera synchronisation, images acquisition and reconstruction, and illumination setup. It is hoped that the presented findings establish better understanding of the setup influences in range gated reconstruction and contribute to optimise the system performance.

Accuracy is an important measure of system performance and remains a challenge in 3D range gated reconstruction despite the advancement in laser and sensor technology. The weighted average model that is commonly used for range estimation is heavily influenced by the intensity variation due to various factors. Accuracy improvement in term of range estimation is therefore important to fully optimise the system performance. In this paper, a 3D range gated reconstruction model is derived based on the operating principles of range gated imaging and time slicing reconstruction, fundamental of radiant energy, Laser Detection And Ranging (LADAR), and Bidirectional Reflection Distribution Function (BRDF). Accordingly, a new range estimation model is proposed to alleviate the effects induced by distance, target reflection, and range distortion. From the experimental results, the proposed model outperforms the conventional weighted average model to improve the range estimation for better 3D reconstruction. The outcome demonstrated is of interest to various laser ranging applications and can be a reference for future works.

Under local thermal non-equilibrium and isoflux boundary conditions, the two-energy-equation model is employed to investigate the effect of viscous dissipation on the thermal characteristics of nanofluid flow through a porous medium embedded in a microchannel. Analytical closed-form solutions of the two-dimensional temperature distributions are obtained for the models with and without the viscous dissipation terms in the energy equation. The analysis emphasizes on the disparities induced by the viscous dissipation between the two models. The use of porous medium is capable to enhance the thermal performance up to 53%. When the viscous dissipation effect is neglected, the thermal performance of nanofluid is overrated as much as 60%, sufficiently serious to trigger an attention in the performance analysis. The heat transfer coefficient of nanofluid is found to be enhanced in the low-Reynolds-number flow regime but it declines in the high-Reynolds-number flow regime. By reducing the size of nanoparticle, the thermal performance can be enhanced as much as 70%. Furthermore, the thermal performance can be further augmented by increasing the channel aspect ratio as well as by increasing the thermal conductivity of the porous material. This study serves as a useful analytical tool for the design and performance characterization of an integrated system incorporating the use of nanofluid and porous medium into a microchannel.

Field-synergy analysis is performed on the viscous dissipative water–alumina nanofluid flow in circular microchannel heat sinks to scrutinize the synergetic relation between the flow and temperature fields for both heating and cooling processes. By varying the Reynolds number and the nanoparticle volume fraction, the effect of viscous dissipation in the convective heat transfer of nanofluid is investigated based on the field synergy principles. For the heating process, under the effect of viscous dissipation, the degree of synergy between the velocity and temperature fields of nanofluid flow deteriorates, leading to a dwindled heat transfer performance of the nanofluid. Due to the presence of two difference heat sources, the synergy angle and field synergy number for viscous dissipative flow are defined to characterize the synergetic behavior. The field synergy in the nanofluid is greater at low-Reynolds-number flow due to the reduced effect of viscous dissipation. By reducing the size of the nanoparticle and increasing the diameter of the microchannel, the degree of synergy between the velocity and temperature fields of the nanofluid flow in microchannel can be intensified, yielding convection heat transfer enhancement. On the other hand, for nanofluid cooling process, the presence of viscous dissipation would augment the field synergy of the flow.

Effects of streamwise conduction on the thermal performance of nanofluid flow in microchannel heat sinks under exponentially decaying wall heat flux are investigated. By employing the first-law principles, models with and without streamwise conduction term in the energy equation are developed for hydrodynamically fully-developed flow. Closed-form solutions are obtained and the analysis emphasizes on the details of discrepancy induced by streamwise conduction between the two models on the heat transport characteristics in nanofluids. The effects of the variations of Peclet number and nanoparticle volume fraction on the thermal characteristics of nanofluid flow in microchannel heat sinks are analyzed and discussed. Due to the tremendous increase in the effective thermal conductivity, the streamwise conduction effect is justified to be more significant in the nanofluid compared to its base fluid. The significance of the streamwise conduction which is prevalent in low-Peclet-number flow is greatly amplified when the volume fraction of nanoparticle is increased. At low Peclet number, the contribution of the streamwise conduction in nanofluid is found to be more than twofold of that in its base fluid. The effect of streamwise conduction on the nanofluid flow in microchannel heat sink is significant albeit not dominant particularly for low Peclet number and high nanoparticle volume fraction of the nanofluid.

The effect of streamwise conduction on the entropy generation of low-Peclet-number nanofluid flow in circular microchannel heat sinks under exponentially decaying wall heat flux with constant pumping power condition is analytically studied. Mathematical models with and without streamwise conduction term in the energy equation are developed and closed-form solutions are obtained. Due to the dramatic increase in the effective thermal conductivity of nanofluids, the streamwise conduction effect is justified to be more significant in the nanofluids compared to their base fluids. The significance of the streamwise conduction which is prevalent in low-Peclet-number flow regime is greatly amplified when the volume fraction of nanoparticle is increased. The thermal characteristics of nanofluids are prominently affected due to the presence of streamwise conduction which consequently alters the characteristics of entropy generation in the second-law analysis. Significant deviations are observed when comparing the cases with and without streamwise conduction. Minimal entropy generation is identified in certain range of the low-Peclet-number flow regime, providing an ideal operating condition from the second-law aspect for nanofluid flow in microchannels. The exergetic effectiveness is also investigated based on the variations on the volume fraction of nanoparticle suspension and the microchannel aspect ratio.

Performance of a range gated system is strongly affected by the laser, sensor, target, and atmospheric parameters. This paper performs a theoretical analysis to investigate the influence of multiple factors on range gated reconstruction. The effects of several factors are discussed based on the operating principle of range gated reconstruction, fundamental of radiant energy, signal to noise ratio (SNR), and bidirectional reflection distribution function (BRDF) models. The presented findings establish a comprehensive understanding of the influence factors in range gated reconstruction which are of interest to various applications and future improvement works to perform accurate range correction and compensation.

This paper performs an experimental investigation on the TOF imaging profile which strongly influences the quality of reconstruction to accomplish accurate range sensing. From our analysis, the reflected intensity profile recorded appears to deviate from Gaussian model which is commonly assumed and can be perceived as a mixture of noises and actual reflected signal. Noise-weighted Average range calculation is therefore proposed to alleviate noise influence based on the signal detection threshold and system noises. From our experimental result, this alternative range solution demonstrates better accuracy as compared to the conventional weighted average method and proven as a para-axial correction to improve range reconstruction in 3D gated imaging system.

The effects of viscous dissipation on the entropy generation of water–alumina nanofluid convection in circular microchannels subjected to exponential wall heat flux are investigated. Closed-form solutions of the temperature distributions in the streamwise direction are obtained for the models with and without viscous dissipation term in the energy equation. The two models are compared by analyzing their relative deviations in entropy generation for different Reynolds numbers and nanoparticle volume fractions. The incorporation of viscous dissipation prominently affects the temperature distribution and consequently the entropy generation. When the viscous dissipation effect is neglected, the total entropy generation and the fluid friction irreversibility are nearly twofold overrated while the heat transfer irreversibility is underestimated significantly. By considering the viscous dissipation effect, the exergetic effectiveness for forced convection of nanofluid in microchannels attenuates with the increasing nanoparticle volume fraction and nanoparticle diameter. The increase in the entropy generation of nanofluid is mainly attributed to the intensification of fluid friction irreversibility. From the aspect of the second-law of thermodynamics, the widespread conjecture that nanofluids possess advantage over pure fluid associated with higher overall effectiveness is invalidated.

An analytical study on the viscous dissipation effect on entropy generation in laminar fully developed forced convection of water–alumina nanofluid in circular microchannels is reported. In the first-law analysis, closed form solutions of the temperature distributions in the radial direction for the models with and without viscous dissipation term in the energy equation are obtained. The results show that the heat transfer coefficient decreases with nanoparticle volume fraction largely in the laminar regime of nanofluid flow in microchannel when the viscous dissipation effect is taken into account. In the second-law analysis, the two models are compared by analyzing their relative deviations in entropy generation for different Reynolds number and nanoparticle volume fraction. When the viscous dissipation is taken into account, the temperature distribution is prominently affected and consequently the entropy generation ascribable to the heat transfer irreversibility is significantly increased. The increase of entropy generation induced by the increase of nanoparticle volume fraction is attributed to the increase of both the thermal conductivity and viscosity of nanofluid which causes augmentation in the heat transfer and fluid friction irreversibilities, respectively. By incorporating the viscous dissipation effect, both thermal performance and exergetic effectiveness for forced convection of nanofluid in microchannels dwindle with nanoparticle volume fraction, contrary to the widespread conjecture that nanofluids possess advantage over pure fluid associated with higher overall effectiveness from the aspects of first-law and second-law of thermodynamics.

This paper is aimed at experimentally developing an in-situ macro-fibre composite (MFCTM) piezoelectric transducer sparse array which functions as both actuator and sensor of Lamb wave for damage detection in composite laminate. Lamb waves which have been used in non-destructive evaluation (NDE) of plate-like structures, can be used for active monitoring and interrogating the health of the structures due to their long range propagation with less attenuation. MFC acting as a powerful actuator of Lamb wave as well as a sensitive sensor is highly conformable and anisotropic in behaviour compared to monolithic piezoelectric transducer. The surface bonded MFC transducer on woven carbon fibre reinforced plastic (CFRP) laminate shows directional Lamb wave generation and reception characteristics. Pitch catch approach is used for low velocity impact damage detection. The MFC sensor shows a drastic drop in signal amplitude with the growth of the impact damage.

The size effect in triggering the actuation of NiTi shape memory alloys directly by electrical current is investigated. Wire/rod is taken as an example in this study to show the relationship between the diameter of shape memory alloy wire/rod and the required current/power for actuation, and in the case of cyclic operation, achievable frequency. Through a few case studies, it is revealed that by presenting on logarithmic scale, the major operating characteristics can be quickly estimated as linear functions of wire/rod diameter.

The propagation behaviour of guided ultrasonic waves in a steel pipe with welded bend is studied by finite element simulation. The effectiveness of the longitudinal L(0,2) and torsional T(0,1) guided waves in detecting circumferential cut near the weld is investigated. In order to identify the presence of the defect, the reflection strength due to the cut is studied. The geometry of the weld is constructed based on common V-bevel butt joints and the anisotropy of the 316L stainless steel weld is included to correctly predict the scattering of ultrasonic waves. The finite element model is built to allow high accuracy. Detection of small circumferential cut (up to 60° circumferential extent) can be achieved with longitudinal L(0,2) mode. Detection of moderate to large circumferential cut can be achieved by torsional T(0,1) or longitudinal L(0,2) modes, with T(0,1) mode preferred due to its less mode conversion to higher order modes.

Piezoelectric bimorphs were assessed for their capabilities to be used as control actuators for vibration suppression of the print circuit boards (PCBs). Plate structures made of FR-4, a widely used industrial-grade material for manufacture of PCBs, were considered. An advanced and structured control algorithm, linear quadratic regulator with output feedback (LQROF), was used for active vibration control of the PCB structures. Experimental results showed that the LQROF control is a more robust algorithm than the classic control using the direct velocity feedback, and piezoelectric bimorph actuators present a great potential for active vibration control of the PCBs, and smart composites with embedded actuators.

The quality of the interfaces in multilayer composites is a critical issue in the reliability testing of the composite product during the manufacturing process and in-service. Weak interfaces have often gone undetected and may become potentially defective at a later stage. One example is the interface between mold compound and silicon (MC/Si) in IC packaging. There is a desire to study the interface quality quantitatively, so the potential defective area can be evaluated and identified early. In this paper, a nondestructive evaluation methodology is proposed to measure the available strength of the interface by using ultrasonic reflection coefficients. It is known that interface degradation can be either due to poor manufacturing process and stress loading. Characterization of the interface quality of the MC/Si interface is first conducted by measuring longitudinal ultrasonic wave reflections from the interface samples fabricated under varying conditioning processes that simulate the degradation. A combined test that measures the reflection coefficient of the interface under stress load has also been conducted to quantify the effect of the load. Finally, it is shown that the overall effect on the reflection coefficient and available strength of the interface is derived and can be used as a quantitative indicator.

Broadband array transducers are widely used in medical imaging systems, and their beam patterns determine the imaging quality. The characteristics of the beam patterns such as mainlobe beamwidth and sidelobe levels are the major criteria for designing and optimizing sparse array systems. The spatial impulse response approach can be used to calculate the beam patterns rigorously in both near field and far field. However, it is time consuming due to the high sampling frequency required, and thus not suitable for array optimization. On the other hand, assuming the array elements to be omnidirectional point sources the field calculation can be much simplified and fast but at the expense of poor accuracy. This paper presents a modified model that has the accuracy comparable to that from the impulse response model while keeping the efficiency close to that of the simple point source model. The developed algorithm is particularly suitable for stochastic methods for two-dimensional (2D) sparse arrays design and optimization such as genetic algorithms (GA), in which the iterative beam pattern calculation dominates the optimization program running time.

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.

Ultrasonic wire bonders with precision capillary tips are widely used for bonding electrical wires to IC chips and circuits. The industry is driving wire-bonding technology towards increased yields, decreased pitch, and ever decreasing cost. However, many technical and material issues will be involved in achieving these goals, such as bond quality monitoring, new failure modes, reliability problems in new plastic mold compounds, and increasing wire sweep problems, in particular lack of the quantitative understanding and validated mathematical model of the bonding process. In this paper, a microslip model is proposed for the bonding process based on the bonding pattern observed, i.e. the wire is bonded at the periphery while the centre is left unbonded. A bilinear hysteresis restoring force is assumed in the microslip model because of its simplicity. The transient displacement response is calculated, and its pattern shows very good agreement with the experiment.

Evaluation of structural intensity in engineering structures is a field of increasing interest in connection with vibration analysis and noise control. In contrast to classical techniques such as modal analysis, structural intensity indicates the magnitude and direction of the vibratory energy travelling in the structures, which yields information about the positions of the sources/sinks, as well as the energy transmission path. Since structural intensity is directly related to the energy level, proper damping treatments and mechanical modifications can then be adopted to dissipate or divert the structure borne sound efficiently and effectively [1]. Since the first introduction and early developments of structural intensity concept [2–4], many measurement methods and numerical prediction approaches have been proposed. For measurement on plate-like structures (plates, shells and their assemblies, etc.), the determination of structural intensity requires the information of surface velocity and stress, as well as the associated phase relationship between them. The initial works [2–4] on structural intensity measurement are mainly conducted with contact transducers such as accelerometers and strain gauges. Later, to overcome the obvious drawbacks of such method, e.g. additional weight introduced by the sensors, non-contact measurement method is proposed based on near-field acoustic [5]. Currently, optical measurement using laser Doppler vibrometer (LDV) or scanning

Ultrasonic C-mode scanning acoustic microscopy (C-SAM) is widely used in the semiconductor industry for reliability testing and product inspection due to its ability to nondestructively detect defects in IC packaging. However, image interpretation and defect identification depend largely on the experience of operators, and there is no defect recognition system; this is partly due to current recognition systems, which are based on computer vision algorithms and are not robust for C-SAM images. A new robust defect recognition system and its application to C-SAM images are described in this paper. The iconic domain of two-dimensional C-SAM grey-level image analysis based on the non-linear Mumford-Shah model is used, and defect recognition is achieved through the use of Support Vector Machines (SVMs). The system is verified through experiments on a sequence of C-SAM images corrupted by synthetically generated noise, bias and different shape. The remarkable defect recognition rates achieved indicate that Support Vector Machines (SVMs) are suitable for IC package defect identification.

In many proposed applications, magnetorheological (MR) fluids are subjected to a dynamic stimulus with finite deformation. Dynamic behavior of reduced iron based MR suspensions under oscillatory shear is experimentally investigated using a parallel-plate rheometer. The effects of strain amplitude, oscillation frequency, and magnetic field strength on the dynamic behavior are studied. MR fluids behave as linear viscoelastic materials for only sufficiently small strain amplitudes. At large strain amplitudes, MR fluids are nonlinear viscoelastic or viscoplastic, where the storage modulus shows a decreasing trend with the strain amplitude. At large enough strain rate amplitudes, the yield stress contribution is negligible and the suspension response is Newtonian. The dependence of the dynamic behavior on the strain amplitude and oscillation frequency is qualitatively summarized in the form of a Pipkin diagram.

This paper presents the design, fabrication and testing of a Magnetorheological (MR) steering damper for motorcycles. After exploring many possible configurations of the MR valve, the proposed design makes sure that the damper is test- and research- friendly in that the damper can be easily assembled and disassembled with simple tools and procedures. The structural and functional integrity of the damper was maintained even with the simple layout of the damper. The dimensions of the MR valve are optimally determined by using finite element analysis. The damper performance under steady shear is experimentally evaluated with an INSTRON test machine. The test results showed that the prototype had fulfilled the basic requirements of the desired MR fluid steering damper.

This paper presents an optimised design of a high-efficiency magnetorheological (MR) valve using finite element analysis. The MR valve is composed of a core, a wound coil, and a cylinder-shaped flux return. The core and flux return form the annulus through which the MR fluid flows. The effects of magnetic field formation mechanism and MR effect formation mechanism on the MR valve performance are investigated. Analytical results of the magnetic flux density in the valve indicate that the saturation in the magnetic flux may be in the core, the flux return, or the valve length. To prevent the saturation as well as to minimise the valve weight, the dimensions of the valve are optimally determined using finite element analysis. In addition, this analysis is coupled with the typical Bingham plastic analysis to predict the MR valve performance.

Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior.

Nonlinear viscoelastic properties of the MR fluid, MRF-132LD, under large-amplitude oscillatory shear were investigated. This was accomplished by carrying out the experiments under the amplitude sweep mode and the frequency sweep mode, using a rheometer with parallel-plate geometry. Investigations under the influence of various magnetic field strength and temperatures were also conducted. MR fluids behave as nonlinear viscoelastic or viscoplastic materials when they are subjected to large-amplitude shear, where the storage modulus decreases rapidly with increasing strain amplitude. Hence, MR fluid behaviour ranges from predominantly elastic at small strain amplitudes to viscous at high strain amplitudes. Large-amplitude oscillatory shear measurements with frequency sweep mode reveal that the storage modulus is independent of oscillation frequency and approaches plateau values at low frequencies. With increasing frequency, the storage modulus shows a decreasing trend before increasing again. This trend may be explained by micro-structural variation. In addition, the storage modulus increases gradually with increasing field strength but it shows a slightly decreasing trend with temperature.

Relaxation experiments under simple step-strain shear were performed on MRF-132LD using a rheometer with parallel-plate geometry. The applied step strains vary from 0.01 to 100%, covering both the pre-yield and post-yield regimes. For small step-strain ranges, the stress relaxation modulus G(t,γ) is independent of step strain, where magnetorheological (MR) fluids behave as linear viscoelastic solids. For large step-strain ranges, the stress relaxation modulus decreases gradually with increasing step strain. Moreover, the stress relaxation modulus G(t,γ) was found to obey time-strain factorability. That is, G(t,γ) can be represented as the product of a linear stress relaxation G(t) and a strain-dependent damping function h(γ). The linear stress relaxation modulus is represented as a three-parameter solid viscoelastic model, and the damping function h(γ) has a sigmoidal form with two parameters. The comparison between the experimental results and the model-predicted values indicates that this model can accurately describe the relaxation behavior of MR fluids under step strains.

BGA (ball-grid array) is an advanced electronic packaging technology that has increasingly become more important and demanding in microelectronic industry. However, no effective technique is available to inspect the performances of the welding points and its co-planarity. The moire fringe method is often employed to measure the three-dimensional (3D) shape of the welding spot on BGA, and a high-resolution CCD camera is utilised to capture the deformation stripe image. In order to gain high measuring accuracy, a frequency-shift moire fringe technique is proposed in this paper, in which three light-sources are deployed to create the fringe. The system parameters are designed to ensure the BGA ball height within exactly one grade moire fringe. By using zero-maximum equation transformation, the measuring range can be segregated into eight subsets. Equal-step interpolation and indexed table approaches are also introduced to greatly improve the measurement speed, so it may be useful for industrial on-line application. Finally, the predicted results based on the simulated images are presented, demonstrating that its measuring accuracy can be achieved to 5 micron.

Displacement-amplifying mechanisms can be systematically designed using topology optimization. Due to the special need for large displacement amplification of piezoelectric stacked actuators, suitable objective functions should be formulated. Among various possible formulations, this work considers maximum output stroke, magnification factor and mechanical efficiency as objective functions. As the formulation of maximum magnification factor performs better numerically than the rest, it is recommended as a suitable design goal for displacement amplifiers undergoing undamped harmonic response. The design problem is solved as a 2D material distribution problem using Method of Moving Asymptotes (MMA). Plane stress solid is assumed for the design domain. Stiffness of the actuator and the workpiece is included in the analysis. To show the viability of this design methodology, two examples of magnification mechanisms for printer heads driven at different excitation frequencies were presented.

An analytical study of the viscous dissipation effect on entropy generation of forced convection of water-alumina nanofluid in a circular microchannel subjected to exponential wall heat flux is reported. Closed form solutions of the temperature distributions in the streamwise direction for the models with and without viscous dissipation term in the energy equation are obtained. The two models are compared by analyzing their relative deviations in entropy generation for different Reynolds number and nanoparticle volume fraction. The incorporation of viscous dissipation prominently affects the temperature distribution and consequently the entropy generation. The increase in the entropy generation is mainly attributable to the increase in the fluid friction irreversibility. The addition of nanoparticle increases the effective thermal conductivity and viscosity of nanofluid which induces escalation in the heat transfer and fluid friction irreversibilities, respectively. By taking the viscous dissipation effect into account, the exergetic effectiveness for forced convection of nanofluid in microchannels attenuate with increasing nanoparticle volume fraction. From the aspect of the second law of thermodynamics, the widespread conjecture that nanofluids possess advantage over pure fluid associated with higher overall effectiveness is invalidated.

A pulsed laser source and a capacitance transducer detector have been used to record the propagation of guided waves in carbon fiber-reinforced polymer composite laminates. Despite the multimode nature of the recorded data, it is shown that the phase velocity dispersion curve of the a/sub 0/ mode can be extracted readily from the waveforms. Experimental dispersion curves have been compared to phase velocity predictions from a global matrix theory. Reasonable correlation between theory and experiment is obtained, demonstrating the validity of the calculations and experimental method.

One of the problems faced in ultrasonic nondestructive testing (NDT) of composite laminates is near-surface delaminations which may be due to impact damage. The normal incidence pulse echo technique has difficulty in resolving echoes from this type of defect since they often lie within the length of the transmitted ultrasonic pulse. Although a high frequency probe may be used, it has its limitations and could be problematic in composite materials in which ply reflections may interfere with defect reflections. The use of an acoustic delay, together with a high frequency probe, may improve the detection. In this paper, a different approach has been developed using the fundamental Lamb wave (S 0 mode) to detect delaminations in unidirectional fibre composite materials. It has been found that the Lamb wave amplitude decreases significantly over a delamination region. The decrease in amplitude is strongly dependent upon the depth of the delamination and is most sensitive to the delaminations near to the surface of the laminate. By scanning the transducer over the surface, it is possible to measure the size and depth of this kind of delamination. This technique is comparable to the delayed pulse echo technique and can be used to complement other techniques.

The range gated technique is a promising laser ranging method that is widely used in different fields such as surveillance, industry, and military. In a range gated system, a reflected laser pulse returned from the target scene contains key information for range reconstruction, which directly affects the system performance. Therefore, it is necessary to study the characteristics and effects of the target reflection factor. In this paper, theoretical and experimental analyses are performed to investigate the influence of target reflection on three-dimensional (3D) range gated reconstruction. Based on laser detection and ranging (LADAR) and bidirectional reflection distribution function (BRDF) theory, a 3D range gated reconstruction model is derived and the effect on range accuracy is analyzed from the perspectives of target surface reflectivity and angle of laser incidence. Our theoretical and experimental study shows that the range accuracy is proportional to the target surface reflectivity, but it decreases when the angle of incidence increases to adhere to the BRDF model. The presented findings establish a comprehensive understanding of target reflection in 3D range gated reconstruction, which is of interest to various applications such as target recognition and object modeling. This paper provides a reference for future improvement to perform accurate range compensation or correction.