To optimize the efficiency of the linear compressor,its operating frequency must be controlled equal to the system resonant frequency.The traditional resonant frequency tracking control algorithm relies on the steady ...To optimize the efficiency of the linear compressor,its operating frequency must be controlled equal to the system resonant frequency.The traditional resonant frequency tracking control algorithm relies on the steady state characteristics of the system,which suffers from slow convergence speed,low accuracy and slow system response.In order to solve these problems,a novel resonant frequency tracking control for linear compressor based on model reference adaptive system(MRAS)is proposed in this paper,and the parameter adaptive rate is derived by the Popov's hyperstability theory,so that the system resonant frequency can be directly calculated through the parameter adaptive rate.Furthermore,the traditional algorithm needs to calculate the piston stroke signal by integrating the back-EMF,which has the problem of integral drift.The algorithm proposed in this paper only needs the velocity signal,and the accuracy of the velocity calculation can be ensured by utilizing the self-adaptive band-pass filter(SABPF),thereby greatly improving the accuracy of the resonance frequency calculation.Simulation results verify the effectiveness of the proposed algorithm.展开更多
A low noise, high conversion gain down-conversion mixer for WLAN 802.11a applications, which adopts the high intermediate frequency （IF） topology, is presented. The input radio frequency （RF）band, local oscillator...A low noise, high conversion gain down-conversion mixer for WLAN 802.11a applications, which adopts the high intermediate frequency （IF） topology, is presented. The input radio frequency （RF）band, local oscillator（LO）frequency band and output IF are 5.15 to 5.35, 4.15 to 4.35 and 1 GHz, respectively. Source resistive degeneration technique and pseudo-differential Gilbert topology are used to achieve high linearity, and, current bleeding technique and LC resonant loads are used to acquire a low noise figure. In addition, the mixer adopts a common-source transistor pair cross-stacked with a source follow pair（CSSF）circuit as an output buffer to enhance the mixer＇s conversion gain but not deteriorate the other performances. The mixer is implemented in 0.18 μm RF CMOS（complementary metal oxide semiconductor transistor）technology and the chip area of the mixer including all bonding pads is 580 μm×1 185 μm. The measured results show that under a 1.8 V supply, the conversion gain is 10.1 dB; the input 1 dB compression point and the input-referred third-order intercept point are-3.5 and 5.3 dBm, respectively; the single side band （SSB）noise figure （NF）is 8.65 dB, and the core current consumption is 3.8 mA.展开更多
This paper presents a new method of High Resolution Range (HRR) profile formation based on Linear Frequency Modulation (LFM) signal fusion of multiple radars with multiple frequency bands. The principle of the multipl...This paper presents a new method of High Resolution Range (HRR) profile formation based on Linear Frequency Modulation (LFM) signal fusion of multiple radars with multiple frequency bands. The principle of the multiple radars signal fusion improving the range resolution is analyzed. With the analysis of return signals received by two radars,it is derived that the phase difference between the echoes varies almost linearly with respect to the frequency if the distance between two radars is neg-ligible compared with the radar observation distance. To compensate the phase difference,an en-tropy-minimization principle based compensation algorithm is proposed. During the fusion process,the B-splines interpolation method is applied to resample the signals for Fourier transform imaging. The theoretical analysis and simulations results show the proposed method can effectively increase signal bandwidth and provide a high resolution range profile.展开更多
As digital image techniques have been widely used, the requirements for high-resolution images become increasingly stringent. Traditional single-frame interpolation techniques cannot add new high frequency information...As digital image techniques have been widely used, the requirements for high-resolution images become increasingly stringent. Traditional single-frame interpolation techniques cannot add new high frequency information to the expanded images, and cannot improve resolution in deed. Multiframe-based techniques are effective ways for high-resolution image reconstruction, but their computation complexities and the difficulties in achieving image sequences limit their applications. An original method using an artificial neural network is proposed in this paper. Using the inherent merits in neural network, we can establish the mapping between high frequency components in low-resolution images and high-resolution images. Example applications and their results demonstrated the images reconstructed by our method are aesthetically and quantitatively (using the criteria of MSE and MAE) superior to the images acquired by common methods. Even for infrared images this method can give satisfactory results with high definition. In addition, a single-layer linear neural network is used in this paper, the computational complexity is very low, and this method can be realized in real time.展开更多
An FSS based circular polarizer for high-speed wireless communication at 75 GHz is presented. It has been designed on a low loss substrate with cross-dipole elements. Both simulation and measured results showed more t...An FSS based circular polarizer for high-speed wireless communication at 75 GHz is presented. It has been designed on a low loss substrate with cross-dipole elements. Both simulation and measured results showed more than 98% circular polarization at 75 GHz. Moreover, 3 dB axial-ratio bandwidth of 6.8 GHz (Simulation) and 7.8 GHz (Measured) has been achieved. The proposed design has many advantages over the recently published research such as simplicity, low-profile, percentage bandwidth, frequency of operation and relative insertion loss.展开更多
A compact 15.0-MeV, 1.5-kW electron linear accelerator(LINAC) was successfully constructed to provide an electron beam for the first photoneutron source at the Shanghai Institute of Applied Physics, Shanghai,China. Th...A compact 15.0-MeV, 1.5-kW electron linear accelerator(LINAC) was successfully constructed to provide an electron beam for the first photoneutron source at the Shanghai Institute of Applied Physics, Shanghai,China. This LINAC consists of five main parts: a thermal cathode grid-controlled electron gun, a pre-buncher, a variable-phase-velocity buncher, a light-speed accelerating structure, and a high-power transportation beamline. A digital feedforward radio frequency compensator is adopted to reduce the energy spread caused by the transient beam loading effect. Furthermore, a real-time electron gun emission feedback algorithm is used to keep the beam stable. After months of efforts, all the beam parameters successfully met the requirements of the facility. In this paper, the beam commissioning process and performance of the LINAC are presented.展开更多
金融市场高频数据包括时间序列数据和其他宏观经济指标,通常具有高维特征.其处理需要更复杂的算法,易产生较高的模型过拟合风险.基于此,提出基于局部线性映射(Local Linear Mapping,LLM)的金融市场波动率高频数据异常检测方法,对各个高...金融市场高频数据包括时间序列数据和其他宏观经济指标,通常具有高维特征.其处理需要更复杂的算法,易产生较高的模型过拟合风险.基于此,提出基于局部线性映射(Local Linear Mapping,LLM)的金融市场波动率高频数据异常检测方法,对各个高频数据目标的日平均序列数据进行标准化处理,在数据筛选时,使用标准化处理设定相关阈值,将不同维度的数据转化为相同的尺度,并利用连通图算法,将具有边连接的金融市场波动率高频数据划分至一个群组内,计算待检测高频数据阈值,采用局部线性映射,完成金融市场波动率高频数据异常检测.实验结果表明:所提方法在TPR为0.98时,ROC曲线稳定运行,贡献因子为1.287,重构误差为1.6%,能够以最快速度使训练集异常检测的损失值达到稳定.展开更多
针对强地物杂波背景下弹载雷达目标检测与识别的技术难题,提出将高分辨距离像(high resolution range profile,HRRP)技术和多普勒波束锐化技术联合对地面进行二维高分辨成像,提高雷达在杂波下目标检测与识别的性能。该方法以线性调频步...针对强地物杂波背景下弹载雷达目标检测与识别的技术难题,提出将高分辨距离像(high resolution range profile,HRRP)技术和多普勒波束锐化技术联合对地面进行二维高分辨成像,提高雷达在杂波下目标检测与识别的性能。该方法以线性调频步进频(linear frequency modulation stepped frequency,LFM-SF)信号为基本波形,首先对平台速度产生的多普勒效应等问题进行了详细讨论并校正;然后通过距离像抽取获得各帧对应的HRRP序列,并采用方位快速傅里叶变换(fast Fourier transform,FFT)实现方位高分辨;最后对实际飞行状态下平台造成的误差进行运动补偿,完成对波束内区域的二维分辨。实测数据的处理验证了所提算法的有效性与实用性。展开更多
热塑性聚乙烯基电缆绝缘材料具有优于交联聚乙烯(cross-linked polyethylene,XLPE)的电气和机械性能,有望成为新一代绿色环保的电缆绝缘材料。在电缆结构设计中,保守的安全绝缘厚度使得电缆的生产成本增加,降低绝缘层的击穿电场强度;并...热塑性聚乙烯基电缆绝缘材料具有优于交联聚乙烯(cross-linked polyethylene,XLPE)的电气和机械性能,有望成为新一代绿色环保的电缆绝缘材料。在电缆结构设计中,保守的安全绝缘厚度使得电缆的生产成本增加,降低绝缘层的击穿电场强度;并且在电缆实际运行过程中,绝缘材料往往工作在70~90℃高温环境下;因此针对新型绝缘材料,温度及厚度对其击穿电场强度的影响研究具有工程实际意义。以线性低密度聚乙烯(linear low density polyethylene,LLDPE)/高密度聚乙烯(high density polyethylene,HDPE)共混绝缘材料为研究对象,进行不同温度下(30、70、90、105℃)及不同厚度下的工频击穿实验,研究温度和厚度对其交流击穿的影响。测试结果表明:相较于XLPE绝缘材料,70L-30H(即LLDPE与HDPE在配比为7∶3的情况下熔融共混得到的绝缘材料)具有较高的工频击穿电场强度,在低于工况温度环境下,其击穿电场强度的温度稳定性较高;然而70L-30H的工频击穿电场强度受厚度影响程度略高,但在相同厚度下其击穿电场强度仍明显高于XLPE。上述研究可为热塑性聚乙烯基电缆绝缘材料研发提供参考。展开更多
基金supported in part by the National Natural Science Foundation of China under Grants 51877093 and 51707079in part by the National Key Research and Development Program of China under Grant 2018YFE0100200in part by the Key Technical Innovation Program of Hubei Province under Grant 2019AAA026.
文摘To optimize the efficiency of the linear compressor,its operating frequency must be controlled equal to the system resonant frequency.The traditional resonant frequency tracking control algorithm relies on the steady state characteristics of the system,which suffers from slow convergence speed,low accuracy and slow system response.In order to solve these problems,a novel resonant frequency tracking control for linear compressor based on model reference adaptive system(MRAS)is proposed in this paper,and the parameter adaptive rate is derived by the Popov's hyperstability theory,so that the system resonant frequency can be directly calculated through the parameter adaptive rate.Furthermore,the traditional algorithm needs to calculate the piston stroke signal by integrating the back-EMF,which has the problem of integral drift.The algorithm proposed in this paper only needs the velocity signal,and the accuracy of the velocity calculation can be ensured by utilizing the self-adaptive band-pass filter(SABPF),thereby greatly improving the accuracy of the resonance frequency calculation.Simulation results verify the effectiveness of the proposed algorithm.
基金The Science and Technology Program of Zhejiang Province (No.2008C16017)
文摘A low noise, high conversion gain down-conversion mixer for WLAN 802.11a applications, which adopts the high intermediate frequency （IF） topology, is presented. The input radio frequency （RF）band, local oscillator（LO）frequency band and output IF are 5.15 to 5.35, 4.15 to 4.35 and 1 GHz, respectively. Source resistive degeneration technique and pseudo-differential Gilbert topology are used to achieve high linearity, and, current bleeding technique and LC resonant loads are used to acquire a low noise figure. In addition, the mixer adopts a common-source transistor pair cross-stacked with a source follow pair（CSSF）circuit as an output buffer to enhance the mixer＇s conversion gain but not deteriorate the other performances. The mixer is implemented in 0.18 μm RF CMOS（complementary metal oxide semiconductor transistor）technology and the chip area of the mixer including all bonding pads is 580 μm×1 185 μm. The measured results show that under a 1.8 V supply, the conversion gain is 10.1 dB; the input 1 dB compression point and the input-referred third-order intercept point are-3.5 and 5.3 dBm, respectively; the single side band （SSB）noise figure （NF）is 8.65 dB, and the core current consumption is 3.8 mA.
文摘This paper presents a new method of High Resolution Range (HRR) profile formation based on Linear Frequency Modulation (LFM) signal fusion of multiple radars with multiple frequency bands. The principle of the multiple radars signal fusion improving the range resolution is analyzed. With the analysis of return signals received by two radars,it is derived that the phase difference between the echoes varies almost linearly with respect to the frequency if the distance between two radars is neg-ligible compared with the radar observation distance. To compensate the phase difference,an en-tropy-minimization principle based compensation algorithm is proposed. During the fusion process,the B-splines interpolation method is applied to resample the signals for Fourier transform imaging. The theoretical analysis and simulations results show the proposed method can effectively increase signal bandwidth and provide a high resolution range profile.
文摘As digital image techniques have been widely used, the requirements for high-resolution images become increasingly stringent. Traditional single-frame interpolation techniques cannot add new high frequency information to the expanded images, and cannot improve resolution in deed. Multiframe-based techniques are effective ways for high-resolution image reconstruction, but their computation complexities and the difficulties in achieving image sequences limit their applications. An original method using an artificial neural network is proposed in this paper. Using the inherent merits in neural network, we can establish the mapping between high frequency components in low-resolution images and high-resolution images. Example applications and their results demonstrated the images reconstructed by our method are aesthetically and quantitatively (using the criteria of MSE and MAE) superior to the images acquired by common methods. Even for infrared images this method can give satisfactory results with high definition. In addition, a single-layer linear neural network is used in this paper, the computational complexity is very low, and this method can be realized in real time.
文摘An FSS based circular polarizer for high-speed wireless communication at 75 GHz is presented. It has been designed on a low loss substrate with cross-dipole elements. Both simulation and measured results showed more than 98% circular polarization at 75 GHz. Moreover, 3 dB axial-ratio bandwidth of 6.8 GHz (Simulation) and 7.8 GHz (Measured) has been achieved. The proposed design has many advantages over the recently published research such as simplicity, low-profile, percentage bandwidth, frequency of operation and relative insertion loss.
基金supported by the Youth Innovation Promotion Association CAS(No.2018300)
文摘A compact 15.0-MeV, 1.5-kW electron linear accelerator(LINAC) was successfully constructed to provide an electron beam for the first photoneutron source at the Shanghai Institute of Applied Physics, Shanghai,China. This LINAC consists of five main parts: a thermal cathode grid-controlled electron gun, a pre-buncher, a variable-phase-velocity buncher, a light-speed accelerating structure, and a high-power transportation beamline. A digital feedforward radio frequency compensator is adopted to reduce the energy spread caused by the transient beam loading effect. Furthermore, a real-time electron gun emission feedback algorithm is used to keep the beam stable. After months of efforts, all the beam parameters successfully met the requirements of the facility. In this paper, the beam commissioning process and performance of the LINAC are presented.
文摘金融市场高频数据包括时间序列数据和其他宏观经济指标,通常具有高维特征.其处理需要更复杂的算法,易产生较高的模型过拟合风险.基于此,提出基于局部线性映射(Local Linear Mapping,LLM)的金融市场波动率高频数据异常检测方法,对各个高频数据目标的日平均序列数据进行标准化处理,在数据筛选时,使用标准化处理设定相关阈值,将不同维度的数据转化为相同的尺度,并利用连通图算法,将具有边连接的金融市场波动率高频数据划分至一个群组内,计算待检测高频数据阈值,采用局部线性映射,完成金融市场波动率高频数据异常检测.实验结果表明:所提方法在TPR为0.98时,ROC曲线稳定运行,贡献因子为1.287,重构误差为1.6%,能够以最快速度使训练集异常检测的损失值达到稳定.
文摘针对强地物杂波背景下弹载雷达目标检测与识别的技术难题,提出将高分辨距离像(high resolution range profile,HRRP)技术和多普勒波束锐化技术联合对地面进行二维高分辨成像,提高雷达在杂波下目标检测与识别的性能。该方法以线性调频步进频(linear frequency modulation stepped frequency,LFM-SF)信号为基本波形,首先对平台速度产生的多普勒效应等问题进行了详细讨论并校正;然后通过距离像抽取获得各帧对应的HRRP序列,并采用方位快速傅里叶变换(fast Fourier transform,FFT)实现方位高分辨;最后对实际飞行状态下平台造成的误差进行运动补偿,完成对波束内区域的二维分辨。实测数据的处理验证了所提算法的有效性与实用性。
文摘热塑性聚乙烯基电缆绝缘材料具有优于交联聚乙烯(cross-linked polyethylene,XLPE)的电气和机械性能,有望成为新一代绿色环保的电缆绝缘材料。在电缆结构设计中,保守的安全绝缘厚度使得电缆的生产成本增加,降低绝缘层的击穿电场强度;并且在电缆实际运行过程中,绝缘材料往往工作在70~90℃高温环境下;因此针对新型绝缘材料,温度及厚度对其击穿电场强度的影响研究具有工程实际意义。以线性低密度聚乙烯(linear low density polyethylene,LLDPE)/高密度聚乙烯(high density polyethylene,HDPE)共混绝缘材料为研究对象,进行不同温度下(30、70、90、105℃)及不同厚度下的工频击穿实验,研究温度和厚度对其交流击穿的影响。测试结果表明:相较于XLPE绝缘材料,70L-30H(即LLDPE与HDPE在配比为7∶3的情况下熔融共混得到的绝缘材料)具有较高的工频击穿电场强度,在低于工况温度环境下,其击穿电场强度的温度稳定性较高;然而70L-30H的工频击穿电场强度受厚度影响程度略高,但在相同厚度下其击穿电场强度仍明显高于XLPE。上述研究可为热塑性聚乙烯基电缆绝缘材料研发提供参考。
