The concept of the time-modulated array has been emerging as an alternative to the complex phase shifters,which lowers the cost of the array feeding network due to the utilization of radio frequency(RF)switches.The va...The concept of the time-modulated array has been emerging as an alternative to the complex phase shifters,which lowers the cost of the array feeding network due to the utilization of radio frequency(RF)switches.The various forms of hexagonal antenna array geometries can be used for applications like surveillance tracking in phased array radar and wireless communication systems.This work proposes the generalized array factor(AF)for the hexagonal antenna array geometry based on time modulation.The time modulation in generalized hexagonal geometry can maintain the fixed static amplitude excitation,giving more flexibility over time.Furthermore,a novel trapezoidal switching function is also proposed and applied to the generalized array factor to enable future researchers to use this array factor in the field of advancement to observe how switching schemes like trapezoidal and rectangular affect the array pattern's side lobe level(SLL).The generalized equation can be utilized for the analysis and synthesis of radiation characteristics of the time-modulated hexagonal array(TMHA),time-modulated concentric hexagonal array(TMCHA),time-modulated hexagonal cylindrical array(TMHCA),and time-modulated hexagonal concentric cylindrical array(TMHCCA).The numerical result illustrates the generation of AF of time-modulated hexagonal structures and also shows that the trapezoidal switching sequence outperforms the rectangular switch using the cat swarm optimization(CSO)approach.展开更多
A hexagon pitch carbon nanotube （CNT） array vertical to the normal gate of cold cathode field emission displayer （FED） is simulated by solving the Laplace equation. The calculated results show that the normal gate...A hexagon pitch carbon nanotube （CNT） array vertical to the normal gate of cold cathode field emission displayer （FED） is simulated by solving the Laplace equation. The calculated results show that the normal gate causes the electric field around the CNT tops to be concentrated and the emission electron beam becomes a column. The field enhancement factor and the emission current intensity step up greatly compared with those of the diode structure. Emission current density increases rapidly with the decrease of normal-gate aperture. The gate voltage exerts a critical influence on the emission current.展开更多
Early equipment fault diagnosis can identify potential risks,significantly reduce maintenance costs,and minimize property damage.However,vibration,strain,and force sensors operating at low frequencies with narrow band...Early equipment fault diagnosis can identify potential risks,significantly reduce maintenance costs,and minimize property damage.However,vibration,strain,and force sensors operating at low frequencies with narrow bandwidths are insufficiently sensitive to fault information,making early fault prediction challenging.Here,we introduce a high-performance,cost-effective,and tiny-sized micro-electromechanical system(MEMS)acoustic emission sensor.This sensor utilizes a 10×11 hexagonal array of piezoelectric micromachined ultrasonic transducers with a chip size of 4 mm×4 mm×0.4 mm.The sensor is encapsulated using an epoxy/Al_(2)O_(3) composite for acoustic impedance matching,and its overall size isΦ16 mm×H 5.5 mm,with a weight of approximately 3 g.This acoustic emission sensor achieves a peak sensitivity of 88.4 dB(ref.V/(m/s))at 335 kHz,and its sensitivity remains above 60 dB across the frequency range from 15 kHz to 620 kHz.In addition,combined with the residual neural networks,an intelligent fault diagnosis of the planetary gear is realized.This MEMS acoustic emission sensor can provide a promising approach for in-situ fault monitoring of highly integrated and miniaturized industrial equipment.展开更多
In this work,evolutionary algorithms are applied for the first time to achieve better radiation characteristics over the conventional beamforming algorithm in the concentric hexagonal antenna array(CHAA),which improve...In this work,evolutionary algorithms are applied for the first time to achieve better radiation characteristics over the conventional beamforming algorithm in the concentric hexagonal antenna array(CHAA),which improves the performance of wireless communication.Multiple signal classification(MUSIC)algorithm is employed for direction of arrival(DoA)estimation.The conventional adaptive beam steering algorithm,least mean-square(LMS)algorithm,is used to steer the beam.Further,the proposed approach is employed by novel particle swarm optimization(NPSO)to reduce sidelobe level(SLL)even further.A six-ring CHAA with 126 elements for DoA estimation and beam steering is simulated.The simulation results of the MUSIC,LMS,NPSO,and particle swarm optimization(PSO)algorithms are provided for various DoAs.展开更多
文摘The concept of the time-modulated array has been emerging as an alternative to the complex phase shifters,which lowers the cost of the array feeding network due to the utilization of radio frequency(RF)switches.The various forms of hexagonal antenna array geometries can be used for applications like surveillance tracking in phased array radar and wireless communication systems.This work proposes the generalized array factor(AF)for the hexagonal antenna array geometry based on time modulation.The time modulation in generalized hexagonal geometry can maintain the fixed static amplitude excitation,giving more flexibility over time.Furthermore,a novel trapezoidal switching function is also proposed and applied to the generalized array factor to enable future researchers to use this array factor in the field of advancement to observe how switching schemes like trapezoidal and rectangular affect the array pattern's side lobe level(SLL).The generalized equation can be utilized for the analysis and synthesis of radiation characteristics of the time-modulated hexagonal array(TMHA),time-modulated concentric hexagonal array(TMCHA),time-modulated hexagonal cylindrical array(TMHCA),and time-modulated hexagonal concentric cylindrical array(TMHCCA).The numerical result illustrates the generation of AF of time-modulated hexagonal structures and also shows that the trapezoidal switching sequence outperforms the rectangular switch using the cat swarm optimization(CSO)approach.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50873047)the Foundation of Gansu Provincial Education Department,China (Grant No. 0603-02)
文摘A hexagon pitch carbon nanotube （CNT） array vertical to the normal gate of cold cathode field emission displayer （FED） is simulated by solving the Laplace equation. The calculated results show that the normal gate causes the electric field around the CNT tops to be concentrated and the emission electron beam becomes a column. The field enhancement factor and the emission current intensity step up greatly compared with those of the diode structure. Emission current density increases rapidly with the decrease of normal-gate aperture. The gate voltage exerts a critical influence on the emission current.
基金supported in part by the National Key Research and Development Program of China(Grant No.2022YFB3205400)in part by the Fundamental Research Funds for the Central Universities(Grant No.2024CDJGF-005)in part by the Science Fund for Distinguished Young Scholars of Chongqing(Grant No.CSTB2022 NSCQJQX0006).
文摘Early equipment fault diagnosis can identify potential risks,significantly reduce maintenance costs,and minimize property damage.However,vibration,strain,and force sensors operating at low frequencies with narrow bandwidths are insufficiently sensitive to fault information,making early fault prediction challenging.Here,we introduce a high-performance,cost-effective,and tiny-sized micro-electromechanical system(MEMS)acoustic emission sensor.This sensor utilizes a 10×11 hexagonal array of piezoelectric micromachined ultrasonic transducers with a chip size of 4 mm×4 mm×0.4 mm.The sensor is encapsulated using an epoxy/Al_(2)O_(3) composite for acoustic impedance matching,and its overall size isΦ16 mm×H 5.5 mm,with a weight of approximately 3 g.This acoustic emission sensor achieves a peak sensitivity of 88.4 dB(ref.V/(m/s))at 335 kHz,and its sensitivity remains above 60 dB across the frequency range from 15 kHz to 620 kHz.In addition,combined with the residual neural networks,an intelligent fault diagnosis of the planetary gear is realized.This MEMS acoustic emission sensor can provide a promising approach for in-situ fault monitoring of highly integrated and miniaturized industrial equipment.
文摘In this work,evolutionary algorithms are applied for the first time to achieve better radiation characteristics over the conventional beamforming algorithm in the concentric hexagonal antenna array(CHAA),which improves the performance of wireless communication.Multiple signal classification(MUSIC)algorithm is employed for direction of arrival(DoA)estimation.The conventional adaptive beam steering algorithm,least mean-square(LMS)algorithm,is used to steer the beam.Further,the proposed approach is employed by novel particle swarm optimization(NPSO)to reduce sidelobe level(SLL)even further.A six-ring CHAA with 126 elements for DoA estimation and beam steering is simulated.The simulation results of the MUSIC,LMS,NPSO,and particle swarm optimization(PSO)algorithms are provided for various DoAs.
