ABSTRACT
Fringe projection profilometry based on structured light has been widely used in 3-D vision due to its advantages of simple structure, good robustness, and high speed. The principle of this technique is to project multiple orders of stripes on the object, and the camera captures the deformed stripe map. Phase unwrapping and depth map calculation are important steps. Still, in actual situations, phase ambiguity is prone to occur at the edges of the object. In this paper, an adaptive phase segmentation and correction (APSC) method after phase unwrapping is proposed. In order to effectively distinguish the stable area and unstable area of the phase, a boundary identification method is proposed to obtain the structural mask of the phase. A phase compensation method is proposed to improve the phase accuracy. Finally, we obtain the 3-D reconstruction result based on the corrected phase. Specific experimental results verify the feasibility and effectiveness of this method.
ABSTRACT
High-quality, stable perovskite films with a wide band gap between 1.65 and 1.80 eV are highly suitable for efficient and cost-competitive silicon-based tandem solar cells. Herein, we demonstrate that the combined strategies of the Pb(SCN)2 additive and air annealing can enable the Cs0.22FA0.78Pb(I0.85Br0.15)3 films with a wide band gap of 1.65 eV and favored properties including pure composition, high crystallinity, micro-sized grains, and reduced defects. With these desired films, the average efficiencies of semitransparent perovskite solar cells (PSCs) are boosted from (18.13 ± 0.31) to (20.35 ± 0.28)%. Further, the semitransparent PSC is used to assemble the four-terminal perovskite/TOPCon tandem solar cell. Benefiting from its excellent performance and preferred optical properties, the obtained tandem solar cell yields a milestone efficiency of 30.32%.
ABSTRACT
Phase-shifting method is widely used in fringe projection profilometry to obtain high-precision wrapped phase maps. The wrapped phase map needs to be converted to an absolute phase map to recover 3D information. The speckle pattern based phase unwrapping method requires only one additional auxiliary pattern, showing great potential for fast 3D measurements. In this paper, a speckle assisted four-steps phase-shifting method was proposed for 3D measurements. This method requires five structured light patterns to complete 3D measurements, including four-steps phase-shifting fringe patterns and a speckle pattern which is used to remove phase ambiguity. The main challenge of speckle based phase unwrapping method is to overcome the mismatch problem which often occurs in some very steep surfaces. In order to improve the speckle matching accuracy, an adaptive horizontal scaling method was proposed. A voting strategy based on phase-connected regions was proposed to reduce the computational overhead. The experiments demonstrate its superior performance, and an accuracy of 0.21 mm was achieved.
ABSTRACT
MEMS-based LiDAR with a low cost and small volume is a promising solution for 3D measurement. In this paper, a reconfigurable angular resolution design method is proposed in a separate-axis Lissajous scanning MEMS LiDAR system. This design method reveals the influence factors on the angular resolution, including the characteristics of the MEMS mirrors, the laser duty cycle and pulse width, the processing time of the echo signal, the control precision of the MEMS mirror, and the laser divergence angle. A simulation was carried out to show which conditions are required to obtain different angular resolutions. The experimental results of the 0.2° × 0.62° and 0.2° × 0.15° (horizontal × vertical) angular resolutions demonstrate the feasibility of the design method to realize a reconfigurable angular resolution in a separate-axis Lissajous scanning MEMS LiDAR system by employing MEMS mirrors with different characteristics. This study provides a reasonable potential to obtain a high and flexible angular resolution for MEMS LiDAR.
ABSTRACT
The efficient manipulation of light-matter interactions in subwavelength all-dielectric nanostructures offers a unique opportunity for the design of novel low-loss visible- and telecom-range nanoantennas for light routing applications. Several studies have achieved longitudinal and transverse light scattering with a proper amplitude and phase balance among the multipole moments excited in dielectric nanoantennas. However, they only involve the interaction between electric dipole, magnetic dipole, and up to the electric quadrupole. Here, we extend and demonstrate a unidirectional transverse light scattering in a V-shaped silicon nanoantenna that involves the balance up to the magnetic quadrupole moment. Based on the long-wavelength approximation and exact multipole decomposition analysis, we find the interference conditions needed for near-unity unidirectional transverse light scattering along with near-zero scattering in the opposite direction. These interference conditions involve relative amplitude and phases of the electromagnetic dipoles and quadrupoles supported by the silicon nanoantenna. The conditions can be applied for the development of either polarization- or wavelength- dependent light routing on a V-shaped silicon and plasmonic nanoantennas.
ABSTRACT
Most of the miniaturized electromagnetic vibrational energy harvesters (EVEHs) are based on oscillating proof mass suspended by several springs or a cantilever structure. Such structural feature limits the miniaturization of the device's footprint. This paper presents an EVEH device based on a torsional vibrating magnet over a stack of flexible planar coils. The torsional movement of the magnet is enabled by microfabricated silicon torsional springs, which effectively reduce the footprint of the device. With a size of 1 cm × 1 cm × 1.08 cm, the proposed EVEH is capable of generating an open-circuit peak-to-peak voltage of 169 mV and a power of 6.9 µW, under a sinusoidal excitation of ±0.5 g (g = 9.8 m/s2) and frequency of 96 Hz. At elevated acceleration levels, the maximum peak-to-peak output voltage is 222 mV under the acceleration of 7 g (±3.5 g).
ABSTRACT
MEMS-based LiDAR (micro-electro-mechanical system based light detection and ranging), with a low cost and small volume, becomes a promising solution for the two-dimensional (2D) and three-dimensional (3D) optical imaging. A semi-coaxial MEMS LiDAR design, based on a synchronous MEMS mirror pair, was proposed in our early study. In this paper, we specifically reveal the synchronization method of the comb-actuated MEMS mirror pair, including the frequency, amplitude, and phase synchronization. The frequency sweeping and phase adjustment are simultaneously implemented to accelerate the MEMS mirror synchronization process. The experiment is set up and the entire synchronization process is completed within 5 s. Eventually, a one-beam MEMS LiDAR system with the synchronous MEMS mirror pair is set up and a LiDAR with a field of view (FOV) of 60°, angular resolution of 0.2°, and frame rate of 360 Hz is obtained. The experimental results verify the feasibility of the MEMS mirror synchronization method and show a promising potential application prospect for the MEMS LiDAR system.
ABSTRACT
This paper presents a low-frequency electromagnetic vibrational energy harvester (EVEH) with two degrees of freedom and two resonant modes. The proposed EVEH is based on a disc magnet suspended in a pendulum fashion by a polymeric spring between two sets of polymer coil stacks. The fabricated EVEH is capable of harvesting vibration energy on two directions with an extended bandwidth. With a sinusoidal acceleration of ±1 g on Z direction, a peak-to-peak closed-circuit output voltage of 0.51 V (open-circuit voltage: 1 V), and an output power of 35.1 µW are achieved at the resonant frequency of 16 Hz. With a sinusoidal acceleration of ±1.5 g on X direction, a peak-to-peak output voltage of 0.14 V and power of 2.56 µW are achieved, at the resonant frequency of 20 Hz.
ABSTRACT
This paper presents a compact electromagnetic vibrational energy harvester (EVEH) with tunable resonance frequency. The resonance frequency of the EVEH is tuned by adjusting the axial stress in the flexible polymeric springs, which is realized by physically pulling and pushing the springs. The stress tuning functionality is realized with a compact structure with small volume. The total frequency tuning range of the proposed EVEH is 56 Hz (74-130 Hz), which is 64% of the natural resonance frequency of the EVEH (88 Hz). It is found that the tensile stress increases the resonance frequency of the EVEH, while the compressive stress firstly reduces the resonance frequency and then increases the resonance frequency due to buckling.
ABSTRACT
A miniaturized reliability test system for microdevices with controlled environmental parameters is presented. The system is capable of measuring key electrical parameters of the microdevices while controlling the environmental conditions around the microdevices. The test system is compact and thus can be integrated with standard test equipment for microdevices. By using a feed-forward decoupling algorithm, the presented test system is capable of generating a temperature range of 0-120 °C and a humidity range of 20-90% RH (0-55 °C), within a small footprint and weight. The accuracy for temperature and humidity control is ±0.1 °C and ±1% RH (30 °C), respectively. The functionality of the proposed test system is verified by integrating it with a piezo shaker to test the environmental reliability of an electromagnetic vibration energy harvester. The proposed system can be used as a proof-of-technology platform for characterizing the performance of microdevices with controlled environmental parameters.
ABSTRACT
Structured light is an optical 3D surface measurement technique with the merits of high speed and high robustness. However, the huge size of traditional digital light processing (DLP) projectors limits its convenience in numerous applications. In this paper, a one-axis MEMS mirror is used as the structured light projector in 3D modeling systems, and has the advantages of small volume and low cost. Limited by the inability to project orthogonal patterns and projection distortion, it is difficult for the one-axis MEMS mirror based 3D modeling system to obtain high accuracy through existing calibration methods. This paper proposed a calibration method for structured light 3D modeling systems that can only project stripes in one direction with projection distortion. A curved surface equation called curved light surface model was proposed to replace the ideal plane equation as the mathematic model of the projected structured light stripes. Experiment results verified that this method can significantly reduce the effect of projection distortion and an accuracy of 0.11 mm was achieved when measuring a standard dumbbell-shaped object with 201.10 mm center-to-center distance.
ABSTRACT
This paper presents a micromachined resonant pressure sensor. The sensor is designed to optimize the sensitivity and reduce the cross-talk between the driving electrodes and sensing electrodes. The relationship between the sensitivity of the sensor and the main design parameters is analyzed both theoretically and numerically. The sensing and driving electrodes are optimized to get both high sensing capacitance and low cross-talk. This sensor is fabricated using a micromachining process based on a silicon-on-insulator (SOI) wafer. An open-loop measurement system and a closed-loop self-oscillation system is employed to measure the characteristics of the sensor. The experiment result shows that the sensor has a pressure sensitivity of about 29 Hz/kPa, a nonlinearity of 0.02%FS, a hysteresis error of 0.05%FS, and a repeatability error of 0.01%FS. The temperature coefficient is less than 2 Hz/°C in the range of -40 to 80 °C and the short-term stability of the sensor is better than 0.005%FS.
