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
A novel see-through display with a liquid crystal lens array was proposed.A liquid crystal Fresnel lens display（LCFLD） with a holographic screen was demonstrated.The proposed display system has high efficiency,simpl...A novel see-through display with a liquid crystal lens array was proposed.A liquid crystal Fresnel lens display（LCFLD） with a holographic screen was demonstrated.The proposed display system has high efficiency,simple fabrication,and low manufacturing cost due to the absence of a polarizer and color filter.展开更多
The full aperture complex amplitude transmittance function of a multi-level diffraction lens with mask- alignment errors was derived based on scalar diffraction theory. The point spread function （PSF） was calculated...The full aperture complex amplitude transmittance function of a multi-level diffraction lens with mask- alignment errors was derived based on scalar diffraction theory. The point spread function （PSF） was calculated by the Kirchhoff diffraction integral. It is found that the radius of the Airy disk increases with the increase of the error in the direction of misalignment, and the image center shifts along the direction of misalignment. A fourlevel diffractive lens with a diameter of 80 mm was fabricated, and its PSF and diffraction efficiency of ＋1st order were calculated and measured. The distribution of PSF is consistent with the calculated results, and the tested diffraction efficiency is slightly smaller than the calculated value; the relative error is 5.71%.展开更多
We demonstrate three-dimensional tomographic imaging vising a Fresnel lens with broadband terahertz pulses. Objects at various locations along the beam propagation path are uniquely imaged on the same imaging plane us...We demonstrate three-dimensional tomographic imaging vising a Fresnel lens with broadband terahertz pulses. Objects at various locations along the beam propagation path are uniquely imaged on the same imaging plane using a Fresnel lens with different frequencies of the imaging beam. This procedure allows the reconstruction of an object's tomographic contrast image by assembling the frequency-dependent images.展开更多
In the present study, a micro-scale solar organic Rankine cycle power generation system was developed. The system comprises of a solar collection system based on compound cylindrical Fresnel lens concentrator and an o...In the present study, a micro-scale solar organic Rankine cycle power generation system was developed. The system comprises of a solar collection system based on compound cylindrical Fresnel lens concentrator and an organic Rankine cycle power generation system integrated with a scroll expander. YD320 and R245 fa were used as the heat transfer fluid and the working fluid, respectively. The effects of the evaporation pressure, the degree of superheat, and the mass flow rate of the working fluid were analyzed to evaluate the solar collection efficiency, the electric power output, the thermal efficiency and exergy efficiency of the system. The results illustrate that both the increasing evaporation pressure and decreasing superheat degree have positive impacts on solar collection efficiency. The electric power increases as the evaporation pressure increases, while the thermal efficiency and the exergy efficiency decrease. However, the system overall efficiency decreases slowly due to the increase of solar collection efficiency. The electric power increases with the increment of the working fluid mass flow rate. The increasing mass flow rate has no visible impact on the thermal and exergy efficiencies of organic Rankine cycle subsystem, whereas a slightly increase of the thermal and exergy efficiencies of the integrated system. The electric power decreases with the increase of the superheat degree, whereas the thermal and the exergy efficiencies of the system increase. The system works more suitably with a higher degree of superheat for the small mass flow rate condition.展开更多
Renewable energies have a high impact on power energy production and reduction of environmental pollution worldwide,so high efforts have been made to improve renewable technologies and research about them.This paper p...Renewable energies have a high impact on power energy production and reduction of environmental pollution worldwide,so high efforts have been made to improve renewable technologies and research about them.This paper presents the thermal performance results obtained by simulation and experimental tests of a parabolic trough collector with central receiver coupled to Fresnel lens,under different configurations on the pipe.The simulation method was computational fluid dynamics(CFD)analysis in SolidWorks(R)soft-ware tool,which works with Naiver-Stokes equations to converge on a solution.Experimental tests were formed with all configurations proposed and three observations for each one,a total of 12 observations were performed in all research.As a result,the best thermal performance in simulation was achieved with the Fresnel lens and black pipe collector,with a maximum temperature of 116℃under 1000 W/m^2 radiation,the same system achieved in experimental tests a maximum temperature of 96℃with a radiation of 983 W/m^2.展开更多
We introduce a dual-polarized(DP)Fabry–Perot cavity(FPC)antenna operating at the millimeter-wave(mmWave)frequency band with high-gain and wideband characteristics.A DP feeding source and a partially reflective surfac...We introduce a dual-polarized(DP)Fabry–Perot cavity(FPC)antenna operating at the millimeter-wave(mmWave)frequency band with high-gain and wideband characteristics.A DP feeding source and a partially reflective surface(PRS)integrated with a Fresnel zone lens are suggested to realize dual-polarization wave radiation over a wide impedance bandwidth.The feeding source provides vertical and horizontal polarizations while keeping high isolation between the two polarizations.PRS is used to realize Fabry cavity to produce a directive beam radiation.The integrated Fresnel zone rings are introduced for phase correction,leading to a significant gain enhancement for the antenna.For verification,a 60-GHz FPC antenna prototype with DP radiation is designed and fabricated with measurement results.It consists of a feeding source,a PRS integrated with a Fresnel zone lens,a quasi-curved reflector,and four three-dimensional printed supporters.The results illustrate that the peak gains of vertical and horizontal polarizations are 18.4 and 17.6 dBi,respectively.The impedance matching bandwidth for the two polarizations is 14%.The performance ensures that the proposed DP FPC antenna is a promising candidate for the fifth-generation wireless communication systems in the mmWave band.展开更多
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 Partner State Key Laboratory on Advanced Displays and Optoelectronics Technologies HKUST,Chinathe National Natural Science Foundation of China(Grant Nos.61435008 and 61575063)the Fundamental Research Funds for the Central Universities,China(Grant No.WM1514036)
文摘A novel see-through display with a liquid crystal lens array was proposed.A liquid crystal Fresnel lens display（LCFLD） with a holographic screen was demonstrated.The proposed display system has high efficiency,simple fabrication,and low manufacturing cost due to the absence of a polarizer and color filter.
基金supported by the National Key R&D Program of China(No.2016YFB0500200)the Key Program of Chinese Academy of Sciences(No.YA16K010)
文摘The full aperture complex amplitude transmittance function of a multi-level diffraction lens with mask- alignment errors was derived based on scalar diffraction theory. The point spread function （PSF） was calculated by the Kirchhoff diffraction integral. It is found that the radius of the Airy disk increases with the increase of the error in the direction of misalignment, and the image center shifts along the direction of misalignment. A fourlevel diffractive lens with a diameter of 80 mm was fabricated, and its PSF and diffraction efficiency of ＋1st order were calculated and measured. The distribution of PSF is consistent with the calculated results, and the tested diffraction efficiency is slightly smaller than the calculated value; the relative error is 5.71%.
文摘We demonstrate three-dimensional tomographic imaging vising a Fresnel lens with broadband terahertz pulses. Objects at various locations along the beam propagation path are uniquely imaged on the same imaging plane using a Fresnel lens with different frequencies of the imaging beam. This procedure allows the reconstruction of an object's tomographic contrast image by assembling the frequency-dependent images.
基金supported by the Beijing Municipal Natural Science Foundation,China(Grant No.3194057)
文摘In the present study, a micro-scale solar organic Rankine cycle power generation system was developed. The system comprises of a solar collection system based on compound cylindrical Fresnel lens concentrator and an organic Rankine cycle power generation system integrated with a scroll expander. YD320 and R245 fa were used as the heat transfer fluid and the working fluid, respectively. The effects of the evaporation pressure, the degree of superheat, and the mass flow rate of the working fluid were analyzed to evaluate the solar collection efficiency, the electric power output, the thermal efficiency and exergy efficiency of the system. The results illustrate that both the increasing evaporation pressure and decreasing superheat degree have positive impacts on solar collection efficiency. The electric power increases as the evaporation pressure increases, while the thermal efficiency and the exergy efficiency decrease. However, the system overall efficiency decreases slowly due to the increase of solar collection efficiency. The electric power increases with the increment of the working fluid mass flow rate. The increasing mass flow rate has no visible impact on the thermal and exergy efficiencies of organic Rankine cycle subsystem, whereas a slightly increase of the thermal and exergy efficiencies of the integrated system. The electric power decreases with the increase of the superheat degree, whereas the thermal and the exergy efficiencies of the system increase. The system works more suitably with a higher degree of superheat for the small mass flow rate condition.
基金supported by Research Vice Rectory of Universidad Militar Nueva Granada-validity,Colombia in 2019(No.IMP-ING-2656).
文摘Renewable energies have a high impact on power energy production and reduction of environmental pollution worldwide,so high efforts have been made to improve renewable technologies and research about them.This paper presents the thermal performance results obtained by simulation and experimental tests of a parabolic trough collector with central receiver coupled to Fresnel lens,under different configurations on the pipe.The simulation method was computational fluid dynamics(CFD)analysis in SolidWorks(R)soft-ware tool,which works with Naiver-Stokes equations to converge on a solution.Experimental tests were formed with all configurations proposed and three observations for each one,a total of 12 observations were performed in all research.As a result,the best thermal performance in simulation was achieved with the Fresnel lens and black pipe collector,with a maximum temperature of 116℃under 1000 W/m^2 radiation,the same system achieved in experimental tests a maximum temperature of 96℃with a radiation of 983 W/m^2.
基金Project supported by the Research Grant Council of the Hong Kong SAR,China(No.CityU11218318)the CityU Strategic Research Grant,China(No.SRG-Fd 7005446)。
文摘We introduce a dual-polarized(DP)Fabry–Perot cavity(FPC)antenna operating at the millimeter-wave(mmWave)frequency band with high-gain and wideband characteristics.A DP feeding source and a partially reflective surface(PRS)integrated with a Fresnel zone lens are suggested to realize dual-polarization wave radiation over a wide impedance bandwidth.The feeding source provides vertical and horizontal polarizations while keeping high isolation between the two polarizations.PRS is used to realize Fabry cavity to produce a directive beam radiation.The integrated Fresnel zone rings are introduced for phase correction,leading to a significant gain enhancement for the antenna.For verification,a 60-GHz FPC antenna prototype with DP radiation is designed and fabricated with measurement results.It consists of a feeding source,a PRS integrated with a Fresnel zone lens,a quasi-curved reflector,and four three-dimensional printed supporters.The results illustrate that the peak gains of vertical and horizontal polarizations are 18.4 and 17.6 dBi,respectively.The impedance matching bandwidth for the two polarizations is 14%.The performance ensures that the proposed DP FPC antenna is a promising candidate for the fifth-generation wireless communication systems in the mmWave band.
