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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.

Compressed sensing leverages the sparsity of signals to reduce the amount of measurements required for its reconstruction. The Shack-Hartmann wavefront sensor meanwhile is a flexible sensor where its sensitivity and dynamic range can be adjusted based on applications. An investigation is done by using compressed sensing in surface measurements with the Shack-Hartmann wavefront sensor. The results show that compressed sensing paired with the Shack-Hartmann wavefront sensor can reliably measure surfaces accurately. The performance of compressed sensing is compared with those of the iterative modal-based wavefront reconstruction and Fourier demodulation of Shack-Hartmann spot images. Compressed sensing performs comparably to the modal based iterative wavefront reconstruction in both simulation and experiment while performing better than the Fourier demodulation in simulation.

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.

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.

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.

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.

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.

Range determination has crucial dependency of intensity over distance due to the fact that output of a range gated system is the reflectivity and range information expressed in term of intensity. From our experimental study, the analyzed trend line of reflected intensity versus range agrees with the theoretical model where it underlies an inverse range-squared dependency. Considering the energy attenuation factor for a better three-dimensional (3D) solution, a range compensation model is derived based on time slicing technique to compensate the effect imposed by distance beyond an optimum range. A range gated imaging system with pulse profile feedback is proposed in order to apply the range compensation model. Experimental results show noticeable improvement as compared to the conventional weighted average method for reflected laser pulse data across different ranges and 3D surface reconstruction using the proposed range compensation model.

Range gated is a laser ranging technique that has been applied in various fields due to its good application prospects. In order to improve the effectiveness of this method, influence factors contributing to the system performance should be well understood. Thus this paper performs theoretical and experimental investigation to comprehend the effects caused by multiple factors on range gated reconstruction. Our study focuses on the distance, target reflection, and acquisition time step parameter where their impacts on the quality of range reconstruction are analyzed. The presented experimental results show the expected trends of range error to support the validity of our theoretical model and discussion which can be used in future improvement works.