The behavior of Schottky contacts in AlGaN/GaN high electron mobility transistors （HEMTs） is investigated by temperature-dependent current-voltage （T-I-V） measurements from 300 K to 473 K. The ideality factor and ...The behavior of Schottky contacts in AlGaN/GaN high electron mobility transistors （HEMTs） is investigated by temperature-dependent current-voltage （T-I-V） measurements from 300 K to 473 K. The ideality factor and barrier height determined based on the thermionic emission （TE） theory are found to be strong functions of temperature, while present a great deviation from the theoretical value, which can be expounded by the barrier height inhomogeneities. In order to determine the forward current transport mechanisms, the experimental data are analyzed using numerical fitting method, considering the temperature-dependent series resistance. It is observed that the current flow at room temperature can be attributed to the tunneling mechanism, while thermionic emission current gains a growing proportion with an increase in temperature. Finally, the effective barrier height is derived based on the extracted thermionic emission component, and an evaluation of the density of dislocations is made from the I-V characteristics, giving a value of 1.49 × 10^7 cm^-2.展开更多
The Magneto-acoustic Tomography with Current Injection (MAT-CI) is a new biological electrical impedance imaging technique that combines Electrical Impedance Tomography (EIT) with Ultrasonic Imaging (UI), which posses...The Magneto-acoustic Tomography with Current Injection (MAT-CI) is a new biological electrical impedance imaging technique that combines Electrical Impedance Tomography (EIT) with Ultrasonic Imaging (UI), which possesses the non-invasive and high-contrast of the EIT and the high-resolution of the UI. The MAT-CI is expected to acquire high quality image and embraces a wide application. Its principle is to put the conductive sample in the Static Magnetic Field(SMF) and inject a time-varying current, during which the SMF and the current interact and generate the Lorentz Force that inspire ultrasonic signal received by the ultrasonic transducers positioned around the sample. And then according to related reconstruction algorithm and ultrasonic signal, electrical conductivity image is obtained. In this paper, a forward problem mathematical model of the MAT-CI has been set up to deduce the theoretical equation of the electromagnetic field and solve the sound source distribution by Green’s function. Secondly, a sound field restoration by Wiener filtering and reconstruction of current density by time-rotating method have deduced the Laplace’s equation that caters to the current density to further acquire the electrical conductivity distribution image of the sample through iteration method. In the end, double-loop coils experiments have been conducted to verify its feasibility.展开更多
为提升综合电能质量调节器(unified power quality conditioner,UPQC)在不同工况下串联侧抗扰动性能,提出一种在abc坐标系下基于电压、电流前馈的复合控制,对传统电网电压前馈进行改进并引入负载电流前馈,以进一步提升控制器动、静态性...为提升综合电能质量调节器(unified power quality conditioner,UPQC)在不同工况下串联侧抗扰动性能,提出一种在abc坐标系下基于电压、电流前馈的复合控制,对传统电网电压前馈进行改进并引入负载电流前馈,以进一步提升控制器动、静态性能。首先,根据UPQC拓扑结构建立串联侧单相数学模型以分析扰动对系统影响;其次,依据数学模型提出改进的复合前馈控制策略;最后,通过实物试验,分别从不同工况验证了该控制策略在UPQC系统中的有效性及优越性。展开更多
As the switching frequency in DC/DC converter increases, original ‘hard-switch’ working mode is not compatible. Another problem is the reliability, which is puzzled in single-ended forward, push-pull or bridge-like ...As the switching frequency in DC/DC converter increases, original ‘hard-switch’ working mode is not compatible. Another problem is the reliability, which is puzzled in single-ended forward, push-pull or bridge-like structures. In this paper, a new dual-ZCS (zero current switches) forward topology is proposed. The operating principle of soft-switch is analyzed, showing the relationship between voltage and current in time domain. Then how to calculate the key parameters of resonant network is . Finally, a prototype ZCS SMPS is implemented and tested. The results consisted with the analyzing results well, and illustrated the advantages of the proposed structure.展开更多
Fouling behavior along the length of membrane module was systematically investigated by performing simple modeling and lab-scale experiments of forward osmosis （FO） membrane process. The flux distribution model deve...Fouling behavior along the length of membrane module was systematically investigated by performing simple modeling and lab-scale experiments of forward osmosis （FO） membrane process. The flux distribution model developed in this study showed a good agreement with experimental results, validating the robustness of the model. This model demonstrated, as expected, that the permeate flux decreased along the membrane channel due to decreasing osmotic pressure differential across the FO membrane. A series of fouling experiments were conducted under the draw and feed solutions at various recoveries simulated by the model. The simulated fouling experiments revealed that higher organic （alginate） fouling and thus more flux decline were observed at the last section of a membrane channel, as foulants in feed solution became more concentrated. Furthermore, the water flux in FO process declined more severely as the recovery increased due to more foulants transported to membrane surface with elevated solute concentrations at higher recovery, which created favorable solution environments for organic adsorption. The fouling reversibility also decreased at the last section of the membrane channel, suggesting that fouling distribution on FO membrane along the module should be carefully examined to improve overall cleaning efficiency. Lastly, it was found that such fouling distribution observed with co-current flow operation became less pronounced in counter- current flow operation of FO membrane process.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.61334002)the Opening Project of Science and Technology on Reliability Physics and Application Technology of Electronic Component Laboratory of China(Grant No.ZHD201206)
文摘The behavior of Schottky contacts in AlGaN/GaN high electron mobility transistors （HEMTs） is investigated by temperature-dependent current-voltage （T-I-V） measurements from 300 K to 473 K. The ideality factor and barrier height determined based on the thermionic emission （TE） theory are found to be strong functions of temperature, while present a great deviation from the theoretical value, which can be expounded by the barrier height inhomogeneities. In order to determine the forward current transport mechanisms, the experimental data are analyzed using numerical fitting method, considering the temperature-dependent series resistance. It is observed that the current flow at room temperature can be attributed to the tunneling mechanism, while thermionic emission current gains a growing proportion with an increase in temperature. Finally, the effective barrier height is derived based on the extracted thermionic emission component, and an evaluation of the density of dislocations is made from the I-V characteristics, giving a value of 1.49 × 10^7 cm^-2.
文摘The Magneto-acoustic Tomography with Current Injection (MAT-CI) is a new biological electrical impedance imaging technique that combines Electrical Impedance Tomography (EIT) with Ultrasonic Imaging (UI), which possesses the non-invasive and high-contrast of the EIT and the high-resolution of the UI. The MAT-CI is expected to acquire high quality image and embraces a wide application. Its principle is to put the conductive sample in the Static Magnetic Field(SMF) and inject a time-varying current, during which the SMF and the current interact and generate the Lorentz Force that inspire ultrasonic signal received by the ultrasonic transducers positioned around the sample. And then according to related reconstruction algorithm and ultrasonic signal, electrical conductivity image is obtained. In this paper, a forward problem mathematical model of the MAT-CI has been set up to deduce the theoretical equation of the electromagnetic field and solve the sound source distribution by Green’s function. Secondly, a sound field restoration by Wiener filtering and reconstruction of current density by time-rotating method have deduced the Laplace’s equation that caters to the current density to further acquire the electrical conductivity distribution image of the sample through iteration method. In the end, double-loop coils experiments have been conducted to verify its feasibility.
文摘为提升综合电能质量调节器(unified power quality conditioner,UPQC)在不同工况下串联侧抗扰动性能,提出一种在abc坐标系下基于电压、电流前馈的复合控制,对传统电网电压前馈进行改进并引入负载电流前馈,以进一步提升控制器动、静态性能。首先,根据UPQC拓扑结构建立串联侧单相数学模型以分析扰动对系统影响;其次,依据数学模型提出改进的复合前馈控制策略;最后,通过实物试验,分别从不同工况验证了该控制策略在UPQC系统中的有效性及优越性。
文摘As the switching frequency in DC/DC converter increases, original ‘hard-switch’ working mode is not compatible. Another problem is the reliability, which is puzzled in single-ended forward, push-pull or bridge-like structures. In this paper, a new dual-ZCS (zero current switches) forward topology is proposed. The operating principle of soft-switch is analyzed, showing the relationship between voltage and current in time domain. Then how to calculate the key parameters of resonant network is . Finally, a prototype ZCS SMPS is implemented and tested. The results consisted with the analyzing results well, and illustrated the advantages of the proposed structure.
基金supported by the World Class University Program (Case Ⅲ) through the National Research Foundation of Koreafunded by the Ministry of Education, Science and Technology (R33-10046)the Fundamental R&D Program for Technology of World Premier Materials funded by the Ministry of Knowledge Economy, Korea
文摘Fouling behavior along the length of membrane module was systematically investigated by performing simple modeling and lab-scale experiments of forward osmosis （FO） membrane process. The flux distribution model developed in this study showed a good agreement with experimental results, validating the robustness of the model. This model demonstrated, as expected, that the permeate flux decreased along the membrane channel due to decreasing osmotic pressure differential across the FO membrane. A series of fouling experiments were conducted under the draw and feed solutions at various recoveries simulated by the model. The simulated fouling experiments revealed that higher organic （alginate） fouling and thus more flux decline were observed at the last section of a membrane channel, as foulants in feed solution became more concentrated. Furthermore, the water flux in FO process declined more severely as the recovery increased due to more foulants transported to membrane surface with elevated solute concentrations at higher recovery, which created favorable solution environments for organic adsorption. The fouling reversibility also decreased at the last section of the membrane channel, suggesting that fouling distribution on FO membrane along the module should be carefully examined to improve overall cleaning efficiency. Lastly, it was found that such fouling distribution observed with co-current flow operation became less pronounced in counter- current flow operation of FO membrane process.
