One of the key challenges in driving multiple light-emitting-diode (LED) strings for a liquid-crystal-display (LCD) backlight system is to ensure uniform current control. Unequal current sharing ...between the strings is due to manufacturing spread and temperature variations. In this paper, a novel current-balancing circuit for LED backlights is proposed. A smart combination of an inherent symmetry of circuit and capacitive balancing mechanism enables an efficient and cost-effective current balancing. The operating principle of the proposed method is analyzed, and an appealing generalization is made. The feasibility of the proposed scheme is verified by developing a hardware prototype with a dimming feature to drive a 100-W edge-type backlight system, having six LED strings for a large-scale LCD panel.
In this paper, an inkjet-printed electromagnet-based touchpad employing spiral resonators is proposed. The proposed touchpad is fabricated by a direct patterning method using an inkjet printer with a ...conductive silver nanoparticle ink. The conductive patterns are easily printed on a paper substrate and sintered for achieving good conductivity. The proposed touchpad is composed of two spiral resonators that resonate at 0.94 GHz (f 1 ) and 1.83 GHz (f 2 ), respectively. When the first resonator is touched, f 1 decreases from 0.94 to 0.81 GHz because of electromagnetic (EM) coupling between the finger and the spiral resonator. Similarly, when the second resonator is touched, f 2 decreases from 1.83 to 1.55 GHz. Owing to the EM coupling distance between the spiral resonator and the finger, the frequency changes although the finger does not reach beyond a height of 1.27 mm on the spiral resonator. The performance of the proposed touchpad is validated using simulation and measurement results.
The harmfulness of fine dust generated by automobile brakes to the environment has recently received attention. Therefore, we aimed to analyze and regulate the brake wear particles in dynamometers. ...To accurately measure the number of particles and particle mass, the sampling system used needs to minimize transportation losses and reduce the residence time in the brake enclosure system. The brake dust measurement system currently used can estimate the main transportation loss but cannot evaluate the complex flow field in the brake enclosure system under different design conditions. We used computational fluid dynamics (CFD) technology to predict the behavior of brake wear particles and analyze the static pressure characteristics, the uniformity of the system flow, and the residence time of the brake dust particles in the system. In addition, we compared the design of the basic structure of the brake enclosure system, combined with the four factors affecting the design of the brake dynamometer, with the enclosure system. As a result, we proposed that the design of the cross section of the brake dynamometer enclosure should be circular, the outlet angle of the enclosure should be 15°, the caliper should be fixed to 150°, and two sets of splitters should be added. This design improves pressure loss and reduces the residence time of brake dust particles in the brake enclosure system.
Abstract
Tunnel oxide passivated contacts (TOPCon) embedding a thin oxide layer between polysilicon and base crystalline silicon have shown great potential in the development of solar cells with high ...conversion efficiency. In this study, we investigate the formation mechanism of hole-carrier selective contacts with TOPCon structure on n-type crystalline silicon wafers. We explore the thermal annealing effects on the passivation properties in terms of the stability of the thermally-formed silicon oxide layer and the deposition conditions of boron-doped polysilicon. To understand the underlying principle of the passivation properties, the active dopant in-diffusion profiles following the thermal annealing are investigated, combined with an analysis of the microscopic structure. Based on PC1D simulation, we find that shallow in-diffusion of boron across a robust tunnel oxide forms a p–n junction and improves the passivation properties. Our findings can provide a pathway to understanding and designing high-quality hole-selective contacts based on the TOPCon structure for the development of highly efficient crystalline silicon solar cells.
In the fabrication of crystalline silicon solar cells, the contact properties between the front metal electrode and silicon are one of the most important parameters for achieving high-efficiency, as ...it is an integral element in the formation of solar cell electrodes. This entails an increase in the surface recombination velocity and a drop in the open-circuit voltage of the solar cell; hence, controlling the recombination velocity at the metal-silicon interface becomes a critical factor in the process. In this study, the distribution of Ag crystallites formed on the silicon-metal interface, the surface recombination velocity in the silicon-metal interface and the resulting changes in the performance of the Passivated Emitter and Rear Contact (PERC) solar cells were analyzed by controlling the firing temperature. The Ag crystallite distribution gradually increased corresponding to a firing temperature increase from 850 ∘C to 950 ∘C. The surface recombination velocity at the silicon-metal interface increased from 353 to 599 cm/s and the open-circuit voltage of the PERC solar cell decreased from 659.7 to 647 mV. Technology Computer-Aided Design (TCAD) simulation was used for detailed analysis on the effect of the surface recombination velocity at the silicon-metal interface on the PERC solar cell performance. Simulations showed that the increase in the distribution of Ag crystallites and surface recombination velocity at the silicon-metal interface played an important role in the decrease of open-circuit voltage of the PERC solar cell at temperatures of 850–900 ∘C, whereas the damage caused by the emitter over fire was determined as the main cause of the voltage drop at 950 ∘C. These results are expected to serve as a steppingstone for further research on improvement in the silicon-metal interface properties of silicon-based solar cells and investigation on high-efficiency solar cells.
Abstract Several biomaterials have been introduced for bone augmentation. However, information is lacking about the mechanisms of bone regeneration and/or integration of these materials in the ...recipient bone. This study aimed to determine the molecular and structural events in bone defects after augmentation with synthetic tetrapod-shaped calcium phosphate (Tetrabone; TetraB) compared with natural deproteinized bovine bone (DBB). Defects were created in the epiphyses of rat femurs and filled with TetraB or DBB or left empty (Sham). After 3, 6, 14 and 28 d, samples were harvested for histology, histomorphometry, ultrastructure and gene expression analyses. At 3 d, higher expressions of bone formation (ALP and OC) and remodeling (CatK) genes were detected in TetraB compared with DBB and Sham. Downregulation of bone remodeling genes (TRAP and CatK) was detected in DBB as compared to Sham after 14 d. Histomorphometry at 6 and 14 d demonstrated greater bone contact with the granules in TetraB. At 28 d, a larger bone area per defect was found in TetraB. The present experiments show that a synthetic substitute, consisting of α-tricalcium and octacalcium phosphates, induces early osteogenic and osteoclastic activities and promotes bone formation in trabecular bone defects.
A thin silicon oxide (SiOx) layer (thickness: 1.5–2.0 nm) formed at an Al2O3/Si interface can enhance the interface properties. However, it is challenging to control the characteristics of thin SiOx ...layers because SiOx forms naturally during Al2O3 deposition on Si substrates. In this study, a ~1.5 nm-thick SiOx layer was inserted between Al2O3 and Si substrates by wet chemical oxidation to improve the passivation properties. The acidic solutions used for wet chemical oxidation were HCl:H2O2:H2O, H2SO4:H2O2:H2O, and HNO3. The thicknesses of SiOx layers formed in the acidic solutions were ~1.48, ~1.32, and ~1.50 nm for SiOx-HCl, SiOx-H2SO4, and SiOx-HNO3, respectively. The leakage current characteristics of SiOx-HNO3 were better than those of the oxide layers formed in the other acidic solutions. After depositing a ~10 nm-thick Al2O3 on an SiOx-acidic/Si structure, we measured the effective carrier lifetime using quasi steady-state photoconductance and examined the interfacial properties of Al2O3/SiOx-acidic/Si using surface carrier lifetime simulation and capacitance–voltage measurement. The effective carrier lifetime of Al2O3/SiOx-HNO3/Si was relatively high (~400 μs), resulting from the low surface defect density (2.35–2.88 × 1010 cm−2eV−1). The oxide layer inserted between Al2O3 and Si substrates by wet chemical oxidation helped improve the Al2O3/Si interface properties.
A novel high-efficiency, compact metamaterial-inspired rectifier is proposed for 900-MHz wireless power transmission (WPT) applications. The open-ended composite right/left-handed (CRLH) transmission ...line (TL) stub, which is introduced to realize metamaterials, replaces the band-pass filter (BPF) of a conventional rectifier (and is smaller than the traditional BPF). The open-ended CRLH TL stub is designed to suppress second- and third-order harmonics and to match the fundamental frequency to a 50-Ω impedance. The device is implemented using lumped elements and a microstrip line. The maximum RF-to-DC conversion efficiency of the proposed rectifier is 69.9% at an input power of 50 mW and a load of 1.8 kΩ. A design procedure that is based on minimizing the phase response of a CRLH TL is presented and validated by simulated and measured results. Because the single CRLH stub is used for harmonic suppression, miniaturization is achieved while retaining efficiency similar to that of previous rectifiers.
In this research, modeling was performed to optimize the grid of the front surface of a solar cell with the passivated emitter and rear contact (PERC) structure by considering the recombination ...characteristics. The front surface recombination velocity can be reduced in two main ways. The first method is to reduce the emitter Auger recombination by lowering the surface doping concentration during emitter formation, and the second method is to reduce the recombination that occurs at the surface when the electrode and the silicon are in contact, which is called metal-induced recombination and is represented by
J
0.metal
. Because
J
0.metal
increases in proportion to the area of the front electrode, minimizing the finger width and number by optimizing the electrode design is important. Therefore, the front electrode grid should be designed considering the emitter characteristics,
J
0.metal
, according to the number of fingers and the resistance. In this research, the front grid of the solar cell was optimized via modeling using equations to calculate the number of fingers and the resistance. According to the finger width, the number of busbars, the sheet resistance, the aspect ratio, and the number of fingers corresponding to the maximum efficiency were identified. As a result, this modeling enabled us to optimize the front grid to the desired conditions, and we found that an increase in the number of busbars plays an important role in improving the efficiency of solar cells. In addition, the efficiency change with increasing number of busbars can be seen to be affected by the width of the finger and the resolution of the printed finger rather than the aspect ratio.
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