So far, the diffracted SAW field generated by an IDT with finite aperture on piezoelectric crystal surfaces is usually analyzed phenomenologically with the angular spectrum theory. A major approximation of this theory...So far, the diffracted SAW field generated by an IDT with finite aperture on piezoelectric crystal surfaces is usually analyzed phenomenologically with the angular spectrum theory. A major approximation of this theory is to ignore the vector nature of the field by assuming that the wave field can be represented by a scalar as in optics. In this paper, a rigorous vector field theory of the surface excitation of elastic wave field in piezoelectric crystal developed by the authors is used to evaluate the SAW diffraction field adepately and precisely. As an example, numerical results for YZ-LiNbO3 are presented and compared with those obtained form the angular spectrum theory.展开更多
The spatiotemporal and spectral characteristics of ultrawide-band terahertz pulses after passing through a Fresnel lens are studied by using the scalar diffraction theory. The simulation shows that the transmitted ter...The spatiotemporal and spectral characteristics of ultrawide-band terahertz pulses after passing through a Fresnel lens are studied by using the scalar diffraction theory. The simulation shows that the transmitted terahertz waveforms compress with increasing propagation distance, and the multi-frequency focusing phenomenon at different focal points is observed. Additionally, the distribution of terahertz fields in a plane perpendicular to the axis is also discussed, and it is found that the diffraction not only induces focusing on-axis but also inhibits focusing at off-axis positions. Therefore, the Fresnel lens may be a useful alternative approach to being a terahertz filter. Moreover, the terahertz pulses travelling as a basic mode of a Gaussian beam are discussed in detail.展开更多
Understanding the physical features of the diffracted sound field on the surface of an axisymmetric body is important for predicting the self-noise of a sonar mounted on an underwater platform. The diffracted sound fi...Understanding the physical features of the diffracted sound field on the surface of an axisymmetric body is important for predicting the self-noise of a sonar mounted on an underwater platform. The diffracted sound field from the transition region of an axisymmetric body was calculated by the geometrical theory of diffraction. The diffraction ray between the source point and the receiving point on the surface of an axisymmetric body was calculated by using the dynamic programming method. Based on the diffracted sound field, a simulation scheme for the noise correlation of the conformal array was presented. It was shown that the normalized pressure of the diffracted sound field from the transition region reduced with the increases of the frequency and the curvature of the ray. The flow noises of two models were compared and a rather optimum fore-body geometric shape was given. Furthermore, it was shown that the correlation of the flow noise in the low frequencies was stronger than that in the high frequencies. And the flow noise received by the acoustic array on the curved surface had a stronger correlation than that on the head plane at the designed center frequency, which is important for sonar system design.展开更多
The directivity of acoustic vector sensor(AVS)will be distorted by the sound diffraction of the AVS carrier.In this paper,the scattering of a plane acoustic wave from a prolate spheroid baffle is considered.At first,t...The directivity of acoustic vector sensor(AVS)will be distorted by the sound diffraction of the AVS carrier.In this paper,the scattering of a plane acoustic wave from a prolate spheroid baffle is considered.At first,the sound diffraction of prolate spheroidal baffle is established,then the mathematical expressions of sound pressure field and particle vibration velocity field of sound diffraction are derived and the characteristic of the directivity of pressure and velocity of sound diffraction field at different frequencies and distances is analyzed.The directivity of AVS is determined by the amplitude and phase difference of diffraction wave and incident wave,which possesses a close relationship with frequency and incident angle.Finally,the calculated results are compared with the experimental results.展开更多
The photo-kinetics of fluorescent molecules have enabled the circumvention of the far-field optical diffraction limit.Despite its enormous potential,the necessity to label the sample may adversely influence the delica...The photo-kinetics of fluorescent molecules have enabled the circumvention of the far-field optical diffraction limit.Despite its enormous potential,the necessity to label the sample may adversely influence the delicate biology under investigation.Thus,continued development efforts are needed to surpass the far-field label-free diffraction barrier.The statistical similarity or finite coherence of the scattered light off the sample in label-free mode hinders the application of existing super-resolution methods based on incoherent fluorescence imaging.In this article,we present physics and propose a methodology to circumvent this challenge by exploiting the photoluminescence(PL)of silicon nitride waveguides for near-field illumination of unlabeled samples.The technique is abbreviated EPSLON,Evanescently decaying Photoluminescence Scattering enables Label-free Optical Nanoscopy.We demonstrate that such an illumination has properties that mimic the photo-kinetics of nano-sized fluorescent molecules,i.e.,such an illumination permits incoherence between the scattered fields from various locations on the sample plane.Thus,the illumination scheme enables the development of a far-field label-free incoherent imaging system that is linear in intensity and stable over time,thereby permitting the application of techniques like structured illumination microscopy(SIM)and intensity-fluctuation-based optical nanoscopy(IFON)in label-free mode to circumvent the diffraction limit.In this proof-of-concept work,we observed a two-point resolution of~180 nm on super-resolved nanobeads and resolution improvements between 1.9×to 2.8×over the diffraction limit,as quantified using Fourier Ring Correlation(FRC),on various biological samples.We believe EPSLON is a step forward within the field of incoherent far-field label-free super-resolution microscopy that holds a key to investigating biological systems in their natural state without the need for exogenous labels.展开更多
基金The project is supported by the National Natural Science Foundation of China
文摘So far, the diffracted SAW field generated by an IDT with finite aperture on piezoelectric crystal surfaces is usually analyzed phenomenologically with the angular spectrum theory. A major approximation of this theory is to ignore the vector nature of the field by assuming that the wave field can be represented by a scalar as in optics. In this paper, a rigorous vector field theory of the surface excitation of elastic wave field in piezoelectric crystal developed by the authors is used to evaluate the SAW diffraction field adepately and precisely. As an example, numerical results for YZ-LiNbO3 are presented and compared with those obtained form the angular spectrum theory.
基金Project supported by the National Basic Research Program of China (Grant Nos 2007CB310408 and 2006CB302901)the National Natural Science Foundation of China (Grant No 10804077)+2 种基金Beijing Municipal Commission of Education (Grant No KM200910028006)Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipalitythe State Key Laboratory of Functional Materials for Informatics,Shanghai Institute of Microsystem and Information Technology,Chinese Academy of Sciences
文摘The spatiotemporal and spectral characteristics of ultrawide-band terahertz pulses after passing through a Fresnel lens are studied by using the scalar diffraction theory. The simulation shows that the transmitted terahertz waveforms compress with increasing propagation distance, and the multi-frequency focusing phenomenon at different focal points is observed. Additionally, the distribution of terahertz fields in a plane perpendicular to the axis is also discussed, and it is found that the diffraction not only induces focusing on-axis but also inhibits focusing at off-axis positions. Therefore, the Fresnel lens may be a useful alternative approach to being a terahertz filter. Moreover, the terahertz pulses travelling as a basic mode of a Gaussian beam are discussed in detail.
基金Project supported by the National Natural Science Foundational of China (Grant No.10774119)the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No.NCET-08-0455)+2 种基金the Natural Science Foundation of Shaanxi Province of China (Grant No.SJ08F07)the Foundation of National Laboratory of Acoustics of Chinathe Foundation for Fundamental Research of Northwestern Polytechnical University of China (Grant No.2007004)
文摘Understanding the physical features of the diffracted sound field on the surface of an axisymmetric body is important for predicting the self-noise of a sonar mounted on an underwater platform. The diffracted sound field from the transition region of an axisymmetric body was calculated by the geometrical theory of diffraction. The diffraction ray between the source point and the receiving point on the surface of an axisymmetric body was calculated by using the dynamic programming method. Based on the diffracted sound field, a simulation scheme for the noise correlation of the conformal array was presented. It was shown that the normalized pressure of the diffracted sound field from the transition region reduced with the increases of the frequency and the curvature of the ray. The flow noises of two models were compared and a rather optimum fore-body geometric shape was given. Furthermore, it was shown that the correlation of the flow noise in the low frequencies was stronger than that in the high frequencies. And the flow noise received by the acoustic array on the curved surface had a stronger correlation than that on the head plane at the designed center frequency, which is important for sonar system design.
文摘The directivity of acoustic vector sensor(AVS)will be distorted by the sound diffraction of the AVS carrier.In this paper,the scattering of a plane acoustic wave from a prolate spheroid baffle is considered.At first,the sound diffraction of prolate spheroidal baffle is established,then the mathematical expressions of sound pressure field and particle vibration velocity field of sound diffraction are derived and the characteristic of the directivity of pressure and velocity of sound diffraction field at different frequencies and distances is analyzed.The directivity of AVS is determined by the amplitude and phase difference of diffraction wave and incident wave,which possesses a close relationship with frequency and incident angle.Finally,the calculated results are compared with the experimental results.
基金This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sktodowska-Curie Grant Agreement No.766181,project"DeLiVER"BSA acknowledges the funding from the Research Council of Norway,projects#NANO 2021-288565 and#BIOTEK 2021-285571from the European InnovationCouncil(EIC),EICTransitionproject#101058016.
文摘The photo-kinetics of fluorescent molecules have enabled the circumvention of the far-field optical diffraction limit.Despite its enormous potential,the necessity to label the sample may adversely influence the delicate biology under investigation.Thus,continued development efforts are needed to surpass the far-field label-free diffraction barrier.The statistical similarity or finite coherence of the scattered light off the sample in label-free mode hinders the application of existing super-resolution methods based on incoherent fluorescence imaging.In this article,we present physics and propose a methodology to circumvent this challenge by exploiting the photoluminescence(PL)of silicon nitride waveguides for near-field illumination of unlabeled samples.The technique is abbreviated EPSLON,Evanescently decaying Photoluminescence Scattering enables Label-free Optical Nanoscopy.We demonstrate that such an illumination has properties that mimic the photo-kinetics of nano-sized fluorescent molecules,i.e.,such an illumination permits incoherence between the scattered fields from various locations on the sample plane.Thus,the illumination scheme enables the development of a far-field label-free incoherent imaging system that is linear in intensity and stable over time,thereby permitting the application of techniques like structured illumination microscopy(SIM)and intensity-fluctuation-based optical nanoscopy(IFON)in label-free mode to circumvent the diffraction limit.In this proof-of-concept work,we observed a two-point resolution of~180 nm on super-resolved nanobeads and resolution improvements between 1.9×to 2.8×over the diffraction limit,as quantified using Fourier Ring Correlation(FRC),on various biological samples.We believe EPSLON is a step forward within the field of incoherent far-field label-free super-resolution microscopy that holds a key to investigating biological systems in their natural state without the need for exogenous labels.
