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The work presented in this paper concerns a method for the miniaturized frequency selective surface (FSS) based on the meander lines. A miniaturized dual-bandstop FSS structure based on meander lines with spiral-shape is proposed and simulated. The equivalent circuit and current distributions are introduced to explain the FSS performance. The size of the unit cell is 10 mm, which is about 0.037 wavelength at the first resonant frequency. Simulation results indicate that the proposed FSS has a frequency shift smaller than 1% for different polarizations with an oblique incident angle of 60°. A prototype of the FSS is fabricated and measured. The measurement results show that the FSS is polarization-insensitive and angle-insensitive.

The air-fuel mixture preparation in pilot spray-ignited natural gas engines is primarily dominated by piston bowl profiles and fuel injection strategy. Piston bowl geometry is regarded as the crucial point in controlling engine pollutant emissions. In the present work, the SAGE combustion model was applied coupled with a general reaction kinetic mechanism. The engine model was validated with experimental data achieved from a Cummins ISX 400 engine, and good agreement between predicted and measured in-cylinder pressure and heat release rate was obtained. The influence of various piston bowl designs, including Mexican-hat geometry, double-lip geometry, bow geometry, and toroidal geometry, on the combustion process, engine performance, and pollutant emissions of a high-pressure direct-injection natural gas engine have been studied and analyzed numerically. The present study confirms the benefit of the piston bowl design as a beneficial tool to enhance the performance and pollutant emissions of the pilot diesel-ignited natural gas engine. Results showed that different chamber shapes slightly influence the combustion initiation, and the difference in in-cylinder pressure presents noticeable as the combustion continues. A higher turbulent kinetic energy improves the flow movement and facilitates the mixture formation in the cylinder. However, the combustion behavior is unwished caused by the improper injection angle of natural gas. Increasing the recess depth of combustion chambers reduces NO

In this paper, Tunnel Oxide Passivated Contact (TOPCon) silicon solar cells with the industrial area (244.32 cm2) are fabricated on N-type silicon substrates. Both the ultra-thin tunnel oxide layer and phosphorus doped polycrystalline silicon (polysilicon) thin film are prepared by the LPCVD system. The wrap-around of polysilicon is observed on the surface of borosilicate glass (BSG). The polysilicon wrap-around can form a leakage current path, thus degrades the shunt resistance of solar cells, and leads to the degradation of solar cell efficiency. Different methods are adopted to treat the polysilicon wrap-around and improve shunt resistance of solar cells. The experimental results indicate that a chemical etching method can effectively solve the problem of polysilicon wrap-around and improve the performance of solar cells. Finally, a conversion efficiency of 22.81% has been achieved by our bifacial TOPCon solar cells, with Voc of 702.6 mV, Jsc of 39.78 mA/cm2 and FF of 81.62%.

Boron doped emitters prepared by thermal diffusion using boron trichloride (BCl3) have been adopted in N-type Tunnel Oxide Passivated Contact (TOPCon) silicon solar cells. In order to establish a proper diffusion process of p + emitter that matches to TOPCon solar cells fabrication, the influence of diffusion pressure, pre-deposition O2 flow rate and drive-in O2 flow rate on the doping profiles, sheet resistance, BSG thickness as well as the sheet resistance uniformity are carefully investigated. In addition, the impact of BSG thickness on the surface morphology and optical properties of the TOPCon cells are studied. The experimental results indicate that good uniformity of p + emitter can be obtained at low pressure (300 mbar) with acceptable sheet resistance. In addition, a p + emitter with thick BSG (> 50 nm) layer is very necessary, which can effectively protect the underneath emitter during the removal process of the wrap-around poly-Si. Finally, high efficiency over 22% is obtained for 244.32 cm2 n-type TOPCon solar cells based on the boron diffused emitter with the sheet resistance 70–90 ohm/sq., BSG thickness ~ 100 nm.

In this article, a compact broadband circularly polarized (CP) antenna with non-planar reflector is presented. In this antenna, two fan-shaped cross-dipoles as the primary radiator and a stepped ground as a reflector are proposed to generate a broadband CP radiation. Besides, four L-shaped patches are introduced to effectively extend the bandwidth (BW) and extract a gain improvement together with the stepped ground. The measured -10 dB impedance BW is 132.08 % (1.36-6.65 GHz) and 3 dB axial ratio (AR) BW is 128.6% (1.39-6.4 GHz), closely with the simulated AR BW 136.73% (1.18-6.28 GHz), showing the proposed antenna features a wider bandwidth, comparing with other broadband CP antennas using similar structures. Due to the compact structure, the overall size of the proposed antenna is only 0.27λl×0.27λl©0.12λl (where λl is the free-space wavelength at 1.36 GHz). The proposed antenna has a wide application scope, such as the wireless network and satellite telecommunications.

A flexible dual-band antenna with a metamaterial structure (MS) is presented. Polyimide substance, which makes the antenna thin and bendable, is used as the substrate for the antenna. When the MS is placed between the antenna and the human’s forearm, the antenna gain is increased by 9.3 and 5.37 dB, and the radiation efficiency is increased by 48.4% and 35.7%, at 2.45 and 5.8 GHz, respectively. In addition, the specific absorption rate is decreased by more than 70%, considering the limitations imposed by Federal Communications Commission and the regulation of International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the frequencies cited above. The fabricated prototype of the antenna with the integrated MS was investigated by placing it on different places of human body, as also on different human bodies. The obtained results show that the proposed antenna is safe and suitable for use, in terms of the ICNIRP standards of World Health Organization.

Mechanical alloying (MA), as one of the main methods of solid state amorphization (SSA), has been intensively used to prepare amorphous alloys. The composition of alloys and processing conditions of MA is very sensitive for the amorphous forming ability (AFA) or/and amorphous forming composition range (AFCR). During the MA processing, the powder was severely plastically deformed and broken into tiny grains with sub-micro or even nano scale size. In this work, a method for AFCR prediction of ternary system has been proposed based on a thermodynamic point of view and including the size-dependent grain boundary energy. The Gibbs free energy (ΔG) of Zr–Fe–Al system has been calculated with the different grain sizes. Compared with the experimental data, the present calculations are reasonable. The present calculations indicate that the smaller the grain size, the wider AFCR for Zr–Fe–Al system is. The present results also indicate that the higher Fe–Zr content alloys have higher AFA, and grain refinement benefits on extending the AFCR.

In this paper, based on cross-dipoles, a right-handed circularly polarized (RHCP) antenna with both broad impedance and axial-ratio (AR) bandwidth is proposed. Moreover, metal vias and branches are loaded to the cross-dipoles aiming to decrease the size of the antenna. The measured results show that a broadband impedance matching bandwidth ranging from 1.83 to 3.42 GHz for S11 less than �10 dB is obtained. Meanwhile, the 3-dB axial-ratio bandwidth is more than 29.0%, and the peak gain of the antenna is about 7.3 dBi with small variation at 2.5 GHz. A prototype is fabricated and measured for validating the design. The good agreements between the simulated and measured results show that the proposed antenna maybe a good candidate in circularly polarized (CP) antenna family.

Tunnel oxide passivated contact (TOPCon) industrial (244.32 cm2) c-Si solar cell is fabricated in this paper. Both the ultra-thin silicon oxide layer and intrinsic polycrystalline silicon layer are deposited by low-pressure chemical vapor deposited (LPCVD). Then intrinsic polycrystalline silicon layers are doped by thermal diffusion of POCl3 in an industrial-scale quartz tube furnace. Experiment conditions like polycrystalline silicon thickness, diffusion temperature, diffusion time and POCL3 flow rate on the passivation quality of TOPCon structure are investigated in detail and low recombination current density ~8 fA/m2 has been achieved for c-Si/SiOx/poly-Si(70 nm)/SiNx structure at diffusion temperature 850 °C. A variation about 30–40 mV has been observed between the iVoc and Voc for 70 nm samples, which should be attributed to the metallization-induced degration. Not consistent with the result obtained from symmetric samples, both an improvement to the solar cell efficiency has been found for 70 nm thick poly-Si and 170 nm thick poly-Si at the diffusion temperature above the optimal diffusion temperature. Finally, by optimizing the polysilion thickness and phosphorus diffusion, the champion solar cell efficiency of 22.81% is achieved, with Voc of 702.6 mV, Jsc of 39.78 mA/cm2, FF of 81.62%.

The development of interdigitated back contact silicon heterojunction has been flourishing in the field of solar cells. The front surface field has a decisive influence on the electrical field effect passivation of interdigitated back contact silicon heterojunction solar cells, and the effect of passivation layers on the performance of solar cells needs to be clarified. In this study, the two-dimension TCAD models of the doped n+-a-Si: H layer and SiNx with a fixed charge layer were established by the Sentaurus code, respectively. The space charge density and electric field intensity, carrier transportation, and distribution of current density were numerically analyzed to evaluate the effect of these two front surfaces on the performance of interdigitated back contact silicon heterojunction solar cells. The results show that for SiNx, the root cause of the field passivation is the surface fixed charge density. The combination of the doping concentration and layer thickness directly affects the field passivation of n+-a-Si: H. Based on the intuitive carrier transport vector, the selective transportation of the carrier near the surface is proved by the front surface field, which effectively inhibits the recombination. The current density distribution on the cross-section reveals that a strong front surface field is an effective way to reduce the internal recombination in particular. Considering practical operating conditions, a doping concentration of 1e20 cm−3, in combination with 7 nm layer thickness, potentially improves the front surface field of n+ a-Si: H leading to the maximum conversion efficiency of 27.41%, with the voltage increased by 32.8 mV and the fill factor reaching 86.84%.

An improved element pattern reconstruction method is introduced to calibrate the mutual coupling effect of antenna arrays, and its applications in wide-angle direction-of-arrival estimation are presented. In this method, direction-of-arrival estimations and a calibration matrix are achieved by alternate iteration. The improved method can achieve a more accurate calibration matrix and direction-of-arrivals with less calculation time and iterations than the joint estimation methods for direction-of-arrivals and calibration matrix. Additionally, the angle ranges of direction-of-arrival estimations can be widened by this method for practical antenna arrays. The validity was verified by some numerical examples with a microstrip antenna array.

An improved mutual coupling calibration approach based on the element pattern reconstruction (EPR) method is proposed in this paper. Compared to previous calibration methods in which the calibration is carried out in the entire space, the space angle ranges to be calibrated in this method is partitioned according to the interested directions. Through the partition of the space angle region, the angle ranges to calibrate are narrowed, and thus more accurate calibration matrix can be obtained in corresponding angle regions. With the employment of the calibration matrix on 2-D DOA estimation, more effective mutual coupling calibration and more accurate DOA estimations are achieved by alternate iteration in each angle region. The validity of this method is verified by an L-shaped microstrip antenna array, and the performance of mutual coupling calibration is presented by the better accuracy in 2-D DOA estimations.

A new mutual coupling compensation method for wideband adaptive arrays is proposed. The new method is developed by combining the element pattern reconstruction method and the cubic Hermit interpolation method to achieve wideband mutual coupling compensation. For the employment of this method, mutual coupling matrices at some frequencies obtained by element pattern reconstruction method are needed and stored. By employing the cubic Hermit interpolation method, all entries of mutual coupling matrix for any frequency within the entire frequency band can be obtained accurately and efficiently. A uniform circular array with eight wideband dipole antennas is designed to verify the validity and effectiveness of the proposed wideband compensation method by the numerical examples.

In this article, a new mutual coupling calibration method, the element pattern reconstruction method, is proposed and utilized to calibrate the mutual coupling effect of circularly polarized microstrip arrays. Previous work has verified that the new calibration method is suitable for arrays composed of not only wire elements but also linearly polarized microstrip elements. The mutual coupling calibration of circularly polarized microstrip arrays employing the new method is presented in this work. For a well-designed circularly polarized microstrip array, the calibration matrix for the main polarization component can be used to calibrate the received signals with high accuracy. The numerical results verify the effectiveness of the new calibration method for the circularly polarized microstrip arrays.

The element pattern reconstruction method is introduced to calibrate the mutual coupling effect of the microstrip arrays. This method is based on the fact that if the reconstructed pattern of the embedded element is consistent with that in the isolated state, then the corresponding calibrated received signal will be consistent with the received signal without mutual coupling effect. The calibration matrix is developed and is employed in the microstrip array to reconstruct the element patterns and in the direction-of-arrival (DOA) estimations. The new method has a wide adaptability for element structures and is very effective for the microstrip antenna array. Effectiveness of the new method is verified by the numerical examples.

For the hydrogen-enriched spark-ignited Wankel engine, the optimization of ignition strategy is conducive to improve combustion performance and specifically effective to lessen the unburned region due to the elongated rotor chamber. In this paper, the role of the number of the ignition source, twin-spark plug location, asynchronous ignition, and energy allocation in improving lean combustion was investigated through the three-dimensional computational fluid dynamics model coupling with kinetic mechanisms. The model was validated by experiment, and good agreements between measured and predicted combustion pressure and the heat release rate was obtained. Results showed that the improvements of engine combustion were limited by single-spark ignition strategies, and the twin-spark ignition configuration was capable of enhancing combustion efficiency drastically. The arrangement of the twin-spark plug determined the space for flame development, and it was favorable for the trailing plug to stand a greater offset from the minor axis of the engine. An earlier leading-spark ignition enabled flame propagation faster and occurred quenching rapidly, which contributed to higher pressure-output and better heat-release. The higher energy of leading-spark ignition made the mixture consumption faster, combustion pressure higher, and combustion duration shorter. The optimum strategy on combustion was expressed as follows: the location of trailing-spark plug is offset from the minor axis by 20.7 mm; the spark timing and discharge energy of leading-spark plug is 325°EA and 0.03 J, respectively; and those of trailing-spark plug is 335°EA and 0.01 J. It was recommended that the leading-spark ignition was set earlier and stronger for practical operations.

Interdigitated back contact silicon hetero-junction (IBC-SHJ) solar cells exhibit excellent performance owing to the IBC and SHJ structures. The front surface field (FSF) layer composed of electric field passivation and chemical passivation has been proved to play an important role in IBC-SHJ solar cells. The electric field passivated layer n+-a-Si: H, an n-type Si alloy with carbon or oxygen in amorphous phase, is simulated in this study to investigate its effect on IBC-SHJ. It is indicated that the n+-a-Si: H layer with wider band gap can reduce the light absorption on the front side efficaciously, which hinders the surface recombination of photo-generated carriers and thus contributes to the improvement of the short circuit current density J sc. The highly doped n+-a-Si: H can result in the remakable energy band bending, which makes it outstanding in the field passivation, while it makes little contribution to the chemical passivation. It is noteworthy that when the electric field intensity exceeds 1.3 × 105 V/cm, the efficiency decrease caused by the inferior chemical passivation is only 0.16%. In this study, the IBC-SHJ solar cell with a front n+-a-Si: H field passivation layer is simulated, which shows the high efficiency of 26% in spite of the inferior chemical passivation on the front surface.

This paper presents a coplanar waveguide (CPW)-fed slot antenna consisting of a slotted ground and a parasitically coupled split ring for multiband operation. In the design, the use of both the loaded split ring to rectangle wide slot and embedded L-slots into the ground is found an effective skill for exciting multiresonant modes as well as miniaturizing the slot antenna. The numerical and experimental results show that the optimal antenna has triple operating bands below – 10-dB reflection coefficients magnitude |S 11|) centered at 2.4/3.5/5.8 GHz covering the required bandwidths of various wireless communication standards. In addition, stable monopole-like radiation patterns and acceptable antenna gains are achieved across the operating bands.

The element pattern reconstruction method is proposed to calibrate the mutual coupling effect of adaptive arrays. The new method is characterized by the wide adaptability for element structures and high accurate calibration of mutual coupling effects. In the development of the new method, the relationship between the element patterns in the isolated state and those in the embedded state is established, and the calibration matrix is obtained by transforming the element patterns of the array. Two compact arrays composed of dipoles and microstrip antennas are designed to testify the effectiveness of the new method. For both arrays, more accurate DOA estimations are obtained due to the element pattern reconstruction method.

A novel compact triple-band slot antenna is proposed for WLAN/WiMAX applications. With the use of three L-shaped slots and an open-ended slot on the ground plane, three resonant modes centered at 2.4/3.5/5.8 GHz are excited. These modes cover the standards of 3.5 GHz WiMAX and 2.4/5.8 GHz WLAN, three useful frequency bands for present wireless communication systems. The proposed antenna fed by L-shaped microstrip line has a small overall dimension of16×30 mm2. The numerical and experimental results show that acceptable radiation characteristic is obtained over the operating bands.

This paper analyzes the suitability of several important parameters which would influence on the signal combining efficiency in antenna arraying techniques. We establish a simulation model in Matlab Simulink environment. The numerical results demonstrate the relationship between the combining loss and each parameter clearly.

This paper studies the wideband signal processing subsystem being designed for antenna arraying techniques. The emphasis is placed on realization structures of the combination algorithm based on the short antenna baselines. A methodology for combining a 100 MHz bandwidth signal at 250 MHz intermediate frequency is presented and a simulation model is built in the Mathworks Simulink environment. It is shown from the simulation results that our method is effective in the wideband signal combining.