A new approach to the study on the transient properties of the levitated object in near-field acoustic levitation （NFAL） is presented. In this article, the transient response characteristics, including the levitated...A new approach to the study on the transient properties of the levitated object in near-field acoustic levitation （NFAL） is presented. In this article, the transient response characteristics, including the levitated height of an object with radius of 24 mm and thickness of 5 mm, the radial velocity and pressure difference of gas at the boundary of clearance between the levitated object and radiating surface （squeeze film）, is calculated according to severa/velocity amplitudes of radiating surface. First, the basic equations in fluid areas on Arbitrary Lagrange--Euler （ALE） form are numericaJly solved by using streamline upwind petrov gaJerkin （SUPG） finite elements method. Second, the formed a/gebraic equations and solid control equations are solved by using synchronous alternating method to gain the transient messages of the levitated object and gas in the squeeze film. Through theoretical and numerical analyses, it is found that there is a oscillation time in the transient process and that the response time does not simply increase with the increasing of velocity amplitudes of radiating surface. More investigations in this paper are helpful for the understanding of the transient properties of levitated object in NFAL, which are in favor of enhancing stabilities and responsiveness of levitated object.展开更多
Ternary layered compound materials(bismuth oxyhalides and metal phosphorus trichalcogenides)stand out in electronic and optoelectronic fields due to their interesting physical properties.However,few studies focus on t...Ternary layered compound materials(bismuth oxyhalides and metal phosphorus trichalcogenides)stand out in electronic and optoelectronic fields due to their interesting physical properties.However,few studies focus on the preparation of high-quality two-dimensional(2D)BiOBr crystals with a typical layered structure,let alone their optoelectronic applications.Here,for the first time,high-quality 2D BiOBr crystals with ultrathin thicknesses(less than 10 nm)and large domain sizes(~100μm)were efficiently prepared via a modified space-confined chemical vapor deposition(SCCVD)method.It is demonstrated that a moderate amount of H2O molecules in the SCCVD system greatly promote the formation of high-quality 2D BiOBr crystals because of the strong polarity of H2O molecules.In addition,a linear relationship between the thickness of BiOBr nanosheets and Raman shift of A1g(1)mode was found.Corresponding theoretical calculations were carried out to verify the experimental data.Furthermore,the BiOBr-based photodetector was fabricated,exhibiting excellent performances with a responsivity of 12.4 A W-1 and a detectivity of 1.6×1013 Jones at 365 nm.This study paves the way for controllable preparation of high-quality 2D BiOBr crystals and implies intriguing opportunities of them in optoelectronic applications.展开更多
基金Supported by the National Basic Research Program of China(973 Program)(2011CB707602)the China Natural Science Fond under Grant No.11174149the Funding of Jiangsu Innovation Program for Graduate Education under Grant No.CXl0B_092Z
文摘A new approach to the study on the transient properties of the levitated object in near-field acoustic levitation （NFAL） is presented. In this article, the transient response characteristics, including the levitated height of an object with radius of 24 mm and thickness of 5 mm, the radial velocity and pressure difference of gas at the boundary of clearance between the levitated object and radiating surface （squeeze film）, is calculated according to severa/velocity amplitudes of radiating surface. First, the basic equations in fluid areas on Arbitrary Lagrange--Euler （ALE） form are numericaJly solved by using streamline upwind petrov gaJerkin （SUPG） finite elements method. Second, the formed a/gebraic equations and solid control equations are solved by using synchronous alternating method to gain the transient messages of the levitated object and gas in the squeeze film. Through theoretical and numerical analyses, it is found that there is a oscillation time in the transient process and that the response time does not simply increase with the increasing of velocity amplitudes of radiating surface. More investigations in this paper are helpful for the understanding of the transient properties of levitated object in NFAL, which are in favor of enhancing stabilities and responsiveness of levitated object.
基金financially supported by the National Natural Science Foundation of China(11674265)the Natural Science Basic Research Project of Shaanxi Province(2018JZ6003)the Fundamental Research Funds for the Central Universities(3102019MS0402)。
文摘Ternary layered compound materials(bismuth oxyhalides and metal phosphorus trichalcogenides)stand out in electronic and optoelectronic fields due to their interesting physical properties.However,few studies focus on the preparation of high-quality two-dimensional(2D)BiOBr crystals with a typical layered structure,let alone their optoelectronic applications.Here,for the first time,high-quality 2D BiOBr crystals with ultrathin thicknesses(less than 10 nm)and large domain sizes(~100μm)were efficiently prepared via a modified space-confined chemical vapor deposition(SCCVD)method.It is demonstrated that a moderate amount of H2O molecules in the SCCVD system greatly promote the formation of high-quality 2D BiOBr crystals because of the strong polarity of H2O molecules.In addition,a linear relationship between the thickness of BiOBr nanosheets and Raman shift of A1g(1)mode was found.Corresponding theoretical calculations were carried out to verify the experimental data.Furthermore,the BiOBr-based photodetector was fabricated,exhibiting excellent performances with a responsivity of 12.4 A W-1 and a detectivity of 1.6×1013 Jones at 365 nm.This study paves the way for controllable preparation of high-quality 2D BiOBr crystals and implies intriguing opportunities of them in optoelectronic applications.
