Similar to air reverberation chambers, non-anechoic water tanks are important acoustic measurement devices that can be used to measure the sound power radiated from complex underwater sound sources using diffusion fie...Similar to air reverberation chambers, non-anechoic water tanks are important acoustic measurement devices that can be used to measure the sound power radiated from complex underwater sound sources using diffusion field theory. However,the problem of the poor applicability of low-frequency measurements in these tanks has not yet been solved. Therefore,we propose a low-frequency acoustic measurement method based on sound-field correction(SFC) in an enclosed space that effectively solves the problem of measuring the sound power from complex sound sources below the Schroeder cutoff frequency in a non-anechoic tank. Using normal mode theory, the transfer relationship between the mean-square sound pressure in an underwater enclosed space and the free-field sound power of the sound source is established, and this is regarded as a correction term for the sound field between this enclosed space and the free field. This correction term can be obtained based on previous measurements of a known sound source. This term can then be used to correct the mean-square sound pressure excited by any sound source to be tested in this enclosed space and equivalently obtain its free-field sound power. Experiments were carried out in a non-anechoic water tank(9.0 m × 3.1 m × 1.7 m) to confirm the validity of the SFC method. Through measurements with a spherical sound source(whose free-field radiation characteristics are known),the correction term of the sound field between this water tank and the free field was obtained. On this basis, the sound power radiated from a cylindrical shell model under the action of mechanical excitation was measured. The measurement results were found to have a maximum deviation of 2.9 d B from the free-field results. These results show that the SFC method has good applicability in the frequency band above the first-order resonant frequency in a non-anechoic tank. This greatly expands the potential low-frequency applications of non-anechoic tanks.展开更多
Acoustic interference of atmosphere has been an attractive research area because of its potential effect on environment,water resources,ecology,agriculture,and other areas.However,it is also a controversial topic beca...Acoustic interference of atmosphere has been an attractive research area because of its potential effect on environment,water resources,ecology,agriculture,and other areas.However,it is also a controversial topic because of the difficulty of quantitative assessment and high operating costs.In this study,a novel acoustic interference technology is proposed that uses strong lowfrequency sound waves.There is no chemical pollution or dependence on airborne vehicles,and it can be remotely controlled at low cost.A complete equipment system for acoustic atmospheric interference technology is established,based on which a series of experimental studies on cloud and precipitation response under acoustic action are performed,mainly including the radar echo intensity,cloud microphysical characteristics and the spatial distribution of ground rainfall intensity.The trigger and periodic effect of the acoustic waves on the cloud are proposed to be the key responses of acoustic atmospheric interference.This study is important to further research on atmosphere interference technology based on low frequency strong sound waves.展开更多
以复杂地形的天津蓟州为例,通过对比距离蓟州最近的大兴探空站资料与欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts, ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料的差异,对基于ERA5资料生成的...以复杂地形的天津蓟州为例,通过对比距离蓟州最近的大兴探空站资料与欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts, ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料的差异,对基于ERA5资料生成的强对流指数在蓟州的适用性进行检验和评估。结果表明:(1)ERA5资料与大兴探空站探测的位势高度、气温和风速在对流层高度吻合,说明ERA5资料能够描述蓟州高空气象条件,且对低空的表现能力比高空准确,各要素中大气湿度的表现相对较差;(2)基于ERA5生成的对流指数中,与强对流天气密切相关的对流有效位能(convective available potential energy, CAPE)、K指数、沙瓦特指数(Showalter index, SI)和大气可降水量(precipitable water, PW)与大兴探空站对应参数的相关系数分别达到0.66、0.90、0.93和0.99,表明利用ERA5构建的对流指数能够揭示大气不稳定层结条件;(3)ERA5对流指数变化与蓟州降水过程相对应,ERA5能够反映天气的变化和发展,为强对流潜势分析提供参考。展开更多
For anti-jamming and anti-countermeasure techniques of the sonar receiver, the response characteristics of the automatic gain control （AGC） circuit and the survivability of the prime circuit under strong interferenc...For anti-jamming and anti-countermeasure techniques of the sonar receiver, the response characteristics of the automatic gain control （AGC） circuit and the survivability of the prime circuit under strong interference are analyzed by simulations and experiments. An AGC simulation model based on the voltage control amplifier VCA810 prototype is proposed. Then static and dynamic simulations are realized with single frequency signal and linear frequency modulated （LFM） signal commonly used in the active sonar. Based on intense sound pulse （ISP） interference experiments, the real-time response characteristics of each module of the receiver are studied to verify the correctness of the model as well as the simulation results. Simulation and experiment results show that, under 252 dB/20 μs ISP interference, the specific sonar receiver will produce sustained cut top oscillation above 30 ms, which may affect the receiver and block the regular sonar signal.展开更多
In order to solve the bad low frequency sound absorption of the Micro-Perforated panel （MPP） absorber, mechanical impedance was introduced in the back of the MPP absorber to form a composite structure. According to ...In order to solve the bad low frequency sound absorption of the Micro-Perforated panel （MPP） absorber, mechanical impedance was introduced in the back of the MPP absorber to form a composite structure. According to the same particle vibration velocity on both sides of a plate, the mechanical impedance plate transfer matrix could be obtained. The units of the mechanical impedance, cavity and MPP were connected in series with the use of the transfer matrix method, thus creating the composite structure＇s theoretical calculation model. The qual- ity factor affecting absorption bandwidth was analyzed. Bandwidth is inversely proportional to the mechanical impedance plate mass. During the experiments, when at close to 400 Hz, the composite structure reached an absorption peak with a coefficient of above 0.8. Experimen- tal results concurred with theoretical calculations. Mechanical resonance is added based on the traditional MPP resonance sound absorption mechanism. Through this, the performance of low frequency sound absorption can be improved without increasing the thickness of the structure. The frequency band can be broadened by reducing the mechanical impedance plate mass and controlling its boundary-damping coefficient.展开更多
In this Letter, we focus on the theoretical analysis of the relativistic energy and angular distributions of the ejected photoelectrons during the relativistic tunnel ionization of atoms by intense, circularly polariz...In this Letter, we focus on the theoretical analysis of the relativistic energy and angular distributions of the ejected photoelectrons during the relativistic tunnel ionization of atoms by intense, circularly polarized light. We make a small modification of the general analytical expressions for these distributions. The role of the initial momentum, the ponderomotive potential, and the Stark shift are considered. We also present the maximal angle of electron emission.展开更多
基金the National Natural Science Foundation of China (Grant No. 11874131)Open Fund Project of Key Laboratory of Underwater Acoustic Countermeasures Technology (Grant No. 2021-JCJQ-LB033-05)。
文摘Similar to air reverberation chambers, non-anechoic water tanks are important acoustic measurement devices that can be used to measure the sound power radiated from complex underwater sound sources using diffusion field theory. However,the problem of the poor applicability of low-frequency measurements in these tanks has not yet been solved. Therefore,we propose a low-frequency acoustic measurement method based on sound-field correction(SFC) in an enclosed space that effectively solves the problem of measuring the sound power from complex sound sources below the Schroeder cutoff frequency in a non-anechoic tank. Using normal mode theory, the transfer relationship between the mean-square sound pressure in an underwater enclosed space and the free-field sound power of the sound source is established, and this is regarded as a correction term for the sound field between this enclosed space and the free field. This correction term can be obtained based on previous measurements of a known sound source. This term can then be used to correct the mean-square sound pressure excited by any sound source to be tested in this enclosed space and equivalently obtain its free-field sound power. Experiments were carried out in a non-anechoic water tank(9.0 m × 3.1 m × 1.7 m) to confirm the validity of the SFC method. Through measurements with a spherical sound source(whose free-field radiation characteristics are known),the correction term of the sound field between this water tank and the free field was obtained. On this basis, the sound power radiated from a cylindrical shell model under the action of mechanical excitation was measured. The measurement results were found to have a maximum deviation of 2.9 d B from the free-field results. These results show that the SFC method has good applicability in the frequency band above the first-order resonant frequency in a non-anechoic tank. This greatly expands the potential low-frequency applications of non-anechoic tanks.
基金supported by the National Key R&D Program of China(Grant No.2017YFC0403600)the National Natural Science Foundation of China(Grant Nos.91847302 and 51879137)+1 种基金the Special Finance of Qinghai Provincethe State Key Laboratory of Hydro-science and Engineering(Grant No.2017-KY-04)。
文摘Acoustic interference of atmosphere has been an attractive research area because of its potential effect on environment,water resources,ecology,agriculture,and other areas.However,it is also a controversial topic because of the difficulty of quantitative assessment and high operating costs.In this study,a novel acoustic interference technology is proposed that uses strong lowfrequency sound waves.There is no chemical pollution or dependence on airborne vehicles,and it can be remotely controlled at low cost.A complete equipment system for acoustic atmospheric interference technology is established,based on which a series of experimental studies on cloud and precipitation response under acoustic action are performed,mainly including the radar echo intensity,cloud microphysical characteristics and the spatial distribution of ground rainfall intensity.The trigger and periodic effect of the acoustic waves on the cloud are proposed to be the key responses of acoustic atmospheric interference.This study is important to further research on atmosphere interference technology based on low frequency strong sound waves.
基金supported by the National Natural Science Foundation of China (10974154)the National Innovation Project of China for Undergraduates (101069935)
文摘For anti-jamming and anti-countermeasure techniques of the sonar receiver, the response characteristics of the automatic gain control （AGC） circuit and the survivability of the prime circuit under strong interference are analyzed by simulations and experiments. An AGC simulation model based on the voltage control amplifier VCA810 prototype is proposed. Then static and dynamic simulations are realized with single frequency signal and linear frequency modulated （LFM） signal commonly used in the active sonar. Based on intense sound pulse （ISP） interference experiments, the real-time response characteristics of each module of the receiver are studied to verify the correctness of the model as well as the simulation results. Simulation and experiment results show that, under 252 dB/20 μs ISP interference, the specific sonar receiver will produce sustained cut top oscillation above 30 ms, which may affect the receiver and block the regular sonar signal.
基金supported by the Scientific Research Foundation for Senior Professional of Jiangsu University(11JDG096)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions((2011)6)
文摘In order to solve the bad low frequency sound absorption of the Micro-Perforated panel （MPP） absorber, mechanical impedance was introduced in the back of the MPP absorber to form a composite structure. According to the same particle vibration velocity on both sides of a plate, the mechanical impedance plate transfer matrix could be obtained. The units of the mechanical impedance, cavity and MPP were connected in series with the use of the transfer matrix method, thus creating the composite structure＇s theoretical calculation model. The qual- ity factor affecting absorption bandwidth was analyzed. Bandwidth is inversely proportional to the mechanical impedance plate mass. During the experiments, when at close to 400 Hz, the composite structure reached an absorption peak with a coefficient of above 0.8. Experimen- tal results concurred with theoretical calculations. Mechanical resonance is added based on the traditional MPP resonance sound absorption mechanism. Through this, the performance of low frequency sound absorption can be improved without increasing the thickness of the structure. The frequency band can be broadened by reducing the mechanical impedance plate mass and controlling its boundary-damping coefficient.
基金supported by the Serbian Ministry of Education,Science,and Technological Development for financial support through Projects 171020 and 171021
文摘In this Letter, we focus on the theoretical analysis of the relativistic energy and angular distributions of the ejected photoelectrons during the relativistic tunnel ionization of atoms by intense, circularly polarized light. We make a small modification of the general analytical expressions for these distributions. The role of the initial momentum, the ponderomotive potential, and the Stark shift are considered. We also present the maximal angle of electron emission.
