This paper presents ambient noise analysis during rough weather, using time series measurements from an automated noise measurement system in the shallow southwest Bay of Bengal during October–November 2010. The peri...This paper presents ambient noise analysis during rough weather, using time series measurements from an automated noise measurement system in the shallow southwest Bay of Bengal during October–November 2010. The period witnessed low-pressure events including depressions and cyclones, with JAL cyclone passing close to the measurement site. The time series noise level shows a shift in mid-October, after which deep depressions and cyclones formed, with an average increase of 5–10 dB in the lower band and 2–3 dB in the higher band of frequencies. Furthermore, correlation between noise level and wave height(data from wave rider buoy deployed at the site) for sea state scale 3 and above shows good correlation with an increase in noise level with increase in wave height, the effect being most pronounced at 0.5 kHz. The noise captured during JAL was analysed to identify the spectrum components due to convective precipitation and heavy wind/wave activity and shows anomalously high levels during the crossing of the cyclone. Rain noise spectra from the rain bands associated with the wall of the cyclone are reported. This has been correlated with radar refl ectivity measurements to ascertain the presence of rain, and discriminate between convective and stratiform types. Also, vertical directionality pattern of ambient noise during JAL showed clearly distinct surface contributions. On the whole, knowledge of ambient noise fields during high sea states and precipitation is useful in optimizing SONAR performance. The findings at the study site have been compared with measurements from other shallow water locations during rough weather.展开更多
Surface acoustic wave （SAW） sensors and micro-electromechanical system （MEMS） technology provide a promising solution for measurement in harsh environments such as gas turbines. In this paper, a SAW resonator （s...Surface acoustic wave （SAW） sensors and micro-electromechanical system （MEMS） technology provide a promising solution for measurement in harsh environments such as gas turbines. In this paper, a SAW resonator （size： 1107μm× 721 μm） based on the AlN/4H-SiC multilayer structure is designed and simulated. A MEMS-compatible fabrication process is employed to fabricate the resonator. The results show that highly c-axis-oriented AlN thin films deposited on the 4H-SiC substrate are obtained, with that the diffraction peak of AlN is 36.10° and the lowest full width at half maximum （FWHM） value is only 1.19°. The test results of the network analyzer are consistent with the simulation curve, which is very encouraging and indicates that our work is a significant attempt to solve the measurement problems mainly including high temperature stability of sensitive structures and the heat transmission of leads in harsh environments. It is essential to get the best performance of SAW resonator, optimize and characterize the behaviors in high temperatures in future research.展开更多
Poly(p-phenylene-2,6-benzobisoxazole)nanofiber(PNF)paper is facing unprecedented challenges in enhancing the interaction between the PNFs and improving its hydrophobicity.In this work,a sol–gel film transformation ap...Poly(p-phenylene-2,6-benzobisoxazole)nanofiber(PNF)paper is facing unprecedented challenges in enhancing the interaction between the PNFs and improving its hydrophobicity.In this work,a sol–gel film transformation approach was developed to fabricate high-strength PNF paper.Iron ions formed coordination bonds between PNFs to obtain a preforming three-dimensional,interconnective nanofiber network.Subsequently,polytetrafluoroethylene(PTFE)particles were sprayed onto the surface of the paper,followed by thermal treatment to obtain double-layered PTFE-P/PNF nanocomposite paper.The nanocomposite paper presents incredible tensile strength(271.6 MPa,increased by 52.9%),folding endurance,super-hydrophobicity,and self-cleaning performances.Moreover,it exhibits low dielectric constant(2.06)and dielectric loss tangent(0.0133)values.According to the wave-transparent model for a doublelayered dielectric established by Maxwell’s equations,the wave-transparent coefficients of electromagnetic waves incident from both sides of the paper are 97.6%(PNF side)and 96.0%(PTFE/P(S-co-BCB-coMMA)side),respectively.The PTFE-P/PNF nanocomposite paper possesses great potential in the fields of wave-transparent applications.展开更多
文摘This paper presents ambient noise analysis during rough weather, using time series measurements from an automated noise measurement system in the shallow southwest Bay of Bengal during October–November 2010. The period witnessed low-pressure events including depressions and cyclones, with JAL cyclone passing close to the measurement site. The time series noise level shows a shift in mid-October, after which deep depressions and cyclones formed, with an average increase of 5–10 dB in the lower band and 2–3 dB in the higher band of frequencies. Furthermore, correlation between noise level and wave height(data from wave rider buoy deployed at the site) for sea state scale 3 and above shows good correlation with an increase in noise level with increase in wave height, the effect being most pronounced at 0.5 kHz. The noise captured during JAL was analysed to identify the spectrum components due to convective precipitation and heavy wind/wave activity and shows anomalously high levels during the crossing of the cyclone. Rain noise spectra from the rain bands associated with the wall of the cyclone are reported. This has been correlated with radar refl ectivity measurements to ascertain the presence of rain, and discriminate between convective and stratiform types. Also, vertical directionality pattern of ambient noise during JAL showed clearly distinct surface contributions. On the whole, knowledge of ambient noise fields during high sea states and precipitation is useful in optimizing SONAR performance. The findings at the study site have been compared with measurements from other shallow water locations during rough weather.
基金Project supported by the Tsinghua University Initiative Scientific Research Program(No.20131089351),China
文摘Surface acoustic wave （SAW） sensors and micro-electromechanical system （MEMS） technology provide a promising solution for measurement in harsh environments such as gas turbines. In this paper, a SAW resonator （size： 1107μm× 721 μm） based on the AlN/4H-SiC multilayer structure is designed and simulated. A MEMS-compatible fabrication process is employed to fabricate the resonator. The results show that highly c-axis-oriented AlN thin films deposited on the 4H-SiC substrate are obtained, with that the diffraction peak of AlN is 36.10° and the lowest full width at half maximum （FWHM） value is only 1.19°. The test results of the network analyzer are consistent with the simulation curve, which is very encouraging and indicates that our work is a significant attempt to solve the measurement problems mainly including high temperature stability of sensitive structures and the heat transmission of leads in harsh environments. It is essential to get the best performance of SAW resonator, optimize and characterize the behaviors in high temperatures in future research.
基金supported by the National Scientific Research Project(Basis Strengthening Plan)China Postdoctoral Science Foundation(2019M653735)+2 种基金State Key Laboratory of Solidification Processing at the Northwestern Polytechnical University(NPU)(SKLSP202103)the Innovation Foundation for Doctor’s Dissertations of NPU(CX2021036)financially supported by the Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars。
文摘Poly(p-phenylene-2,6-benzobisoxazole)nanofiber(PNF)paper is facing unprecedented challenges in enhancing the interaction between the PNFs and improving its hydrophobicity.In this work,a sol–gel film transformation approach was developed to fabricate high-strength PNF paper.Iron ions formed coordination bonds between PNFs to obtain a preforming three-dimensional,interconnective nanofiber network.Subsequently,polytetrafluoroethylene(PTFE)particles were sprayed onto the surface of the paper,followed by thermal treatment to obtain double-layered PTFE-P/PNF nanocomposite paper.The nanocomposite paper presents incredible tensile strength(271.6 MPa,increased by 52.9%),folding endurance,super-hydrophobicity,and self-cleaning performances.Moreover,it exhibits low dielectric constant(2.06)and dielectric loss tangent(0.0133)values.According to the wave-transparent model for a doublelayered dielectric established by Maxwell’s equations,the wave-transparent coefficients of electromagnetic waves incident from both sides of the paper are 97.6%(PNF side)and 96.0%(PTFE/P(S-co-BCB-coMMA)side),respectively.The PTFE-P/PNF nanocomposite paper possesses great potential in the fields of wave-transparent applications.
