Against the backdrop of electromagnetic space integration,the radio system of equipment platforms,such as next-generation aircraft,must possess multifunctional integration and electromagnetic stealth performance.Meanw...Against the backdrop of electromagnetic space integration,the radio system of equipment platforms,such as next-generation aircraft,must possess multifunctional integration and electromagnetic stealth performance.Meanwhile,the equipment platforms need to evolve towards flat structures.These requirements pose significant technical challenges for antenna system design.The antenna must possess ultra-wideband to facilitate multi-function integration through the use of continuous radio frequency synthetic aperture.In order to ensure good aerodynamics of the flat airborne platform,it is required to implement conformal design,while the ultra-low profile is the greatest challenge in conformal design.Against this background,this work proposes a novel airborne tightly coupled antenna with ultra-low profile,ultra-wideband,and vertical-polarized omnidirectional radiation.The antenna unit utilizes a long slot structure and implements circular conformal design,where the resistive frequency selection surface is used to expand the operating bandwidth.This antenna has a profile height of only 0.047 times the low-frequency wavelength.Simulation and measurement results show that it achieves an impedance bandwidth of nearly 12∶1 with omnidirectional beam coverage,which meets the requirements of multifunctional future airborne antennas.展开更多
Inspired by the design philosophy of information metasurfaces based on the digital coding concept,a planar 4-bit reconfigurable antenna array with low profile of 0.15λ0(whereλ0is the free-space wavelength)is present...Inspired by the design philosophy of information metasurfaces based on the digital coding concept,a planar 4-bit reconfigurable antenna array with low profile of 0.15λ0(whereλ0is the free-space wavelength)is presented.The array is based on a digital coding radiation element consisting of a 1-bit magnetoelectric(ME)dipole and a miniaturized reflection-type phase shifter(RTPS).The proposed 1-bit ME dipole can provide two digital states of"0"and"1"(with 0°and 180°phase responses)over a wide frequency band by individually exciting its two symmetrical feeding ports.The designed RTPS is able to realize a relative phase shift of 173°.By digitally quantizing its phase in the range of 157.5°,additional eight digital states at intervals of 22.5°are obtained.To achieve low sidelobe levels,a 1:16 power divider based on the Taylor line source method is employed to feed the array,A prototype of the proposed 4-bit antenna array has been fabricated and tested,and the experimental results are in good agreement with the simulations.Scanning beams within a±45°range were measured with a maximum realized gain of 13.4 dBi at12 GHz.The sidelobe and cross-polarization levels are below-14.3 and-23.0 dB,respectively.Furthermore,the beam pointing error is within 0.8°,and the 3 dB gain bandwidth of the broadside beam is 25%.Due to its outstanding performance,the array holds potential for significant applications in radar and wireless communication systems.展开更多
To protect the driver in case of a tractor overturn,narrow-track tractors,mainly used for working under trees or in vineyards,can be equipped with a foldable roll-over protective structure(FROPS)generally consisting o...To protect the driver in case of a tractor overturn,narrow-track tractors,mainly used for working under trees or in vineyards,can be equipped with a foldable roll-over protective structure(FROPS)generally consisting of a two-pillar front-mounted foldable rollbar.FROPSs have been mainly developed to offer greater mobility when working in low overhead clearance zones(CZs)and more storage options.However,many fatalities and serious injuries in Italy are due to overturn of narrow tractors with FROPS not in safety configuration.The reason lies on that lowering and raising a conventional FROPS is a time-consuming and strenuous process.After operators fold down FROPS to pass a low overhead CZ,some prefer to leave it in the folded or inoperative position,increasing the risk of a roll-over fatality.Italian Workers Compensation Authority(Inail)collects injury reports of workers covered by compulsory accident insurance.However,for agricultural sector Inail set up in 2008 a national observatory to add data and information on fatalities in agriculture covering workers,even those not Inail insured.From these data it appears that about 10 fatalities per year occur in Italy involving folded ROPS.The aim of the analysis in this article is to make a survey on the FROPS issue considering both what is required by Mother Regulation(Regulation(EU)167/2013)for new tractors and the achievable technical solutions to be applied on old tractors for reducing the misuse of FROPS.展开更多
The finding of Snell’s law for anomalous reflection enables broad applications of metasurfaces in stealth,communication,radar technology,etc.However,some unavoidable high-order modes are inherently generated due to t...The finding of Snell’s law for anomalous reflection enables broad applications of metasurfaces in stealth,communication,radar technology,etc.However,some unavoidable high-order modes are inherently generated due to the super lattice of this local approach,which thus causes a decrease in efficiency and a limit in the reflected angle.Here,a novel,to our knowledge,low-profile wideband reflective meta-atom shaped like a four-leaf rose is proposed to achieve a phase coverage of full 360°by varying the length of the rose leaf.Then,the genetic algorithm is adopted for the first time to encode and optimize the topology of each meta-atom on the coding metasurface to achieve two-dimensional(2D)anomalous reflection with excellent performances through an inverse design.Numerical results show that our optimized coding metasurfaces achieve a high-efficiency(≥90%)and large-angle(θ≤70°and 0°≤φ≤360°)reflection under normal incidence.For verification,far-field measurement is carried out and experimental results are consistent with the numerical ones.Our work sets up a solid platform for utilizing algorithms,especially in artificial intelligence,in the future for arbitrary 2D anomalous reflection with high efficiency and a large angle.展开更多
This paper presents a new idea to reduce the solidity of low-pressure turbine(LPT) blade cascades,while remain the structural integrity of LPT blade.Aerodynamic performance of a low solidity LPT cascade was improved b...This paper presents a new idea to reduce the solidity of low-pressure turbine(LPT) blade cascades,while remain the structural integrity of LPT blade.Aerodynamic performance of a low solidity LPT cascade was improved by increasing blade trailing edge thickness(TET).The solidity of the LPT cascade blade can be reduced by about12.5% through increasing the TET of the blade without a significant drop in energy efficiency.For the low solidity LPT cascade,increasing the TET can decrease energy loss by 23.30% and increase the flow turning angle by1.86% for Reynolds number(Re) of 25,000 and freestream turbulence intensities(FSTT) of 2.35%.The flow control mechanism governing behavior around the trailing edge of an LPT cascade is also presented.The results show that appropriate TET is important for the optimal design of high-lift load LPT blade cascades.展开更多
A low-profile cylindrical dielectric resonator antenna(CDRA)with enhanced impedance bandwidth is proposed via sharing a single triple-mode dielectric resonator.Initially,the resonant frequencies of TM01d and TM02d mod...A low-profile cylindrical dielectric resonator antenna(CDRA)with enhanced impedance bandwidth is proposed via sharing a single triple-mode dielectric resonator.Initially,the resonant frequencies of TM01d and TM02d modes of a conventional CDRA are maintained far away from each other under central probe feed.Next,a circular disk with an annular ring is loaded around the conventional CDRA,aiming to excite an additional mode between these dual modes.The electric fields demon-strate that the previous TM_(02δ) mode is transformed into the TM03d mode for the modified CDRA,and an additional TM_(02δ) mode is successfully excited between the TM_(01δ) and TM_(03δ) modes.As a result,the resonant frequencies of these three radiative modes are reallocated in proximity to each other,thus achieving the desired bandwidth enhancement.In addition,considering the small input impedance of the CDRA,a microstrip feeding line is introduced underneath the central probe for good impedance matching.With these arrangements,the resultant antenna can generate an extended bandwidth under simultaneous radiation of TM_(01δ),TM_(02δ),and TM_(03δ) modes.Finally,the proposed CDRA is designed,fabricated,and measured to validate the predicted per-formance.The simulated and measured results show that the impedance bandwidth(|S11|<-10 dB of the antenna is dramatically extended from 8%to about 62%(2.835.36 GHz),while keeping a stable conical radiation pattern.In particular,a low profile property of about 0.15 free space wavelength is achieved as well.展开更多
Microstrip antennas are of significant interest and extensively utilized in communication systems because of their unique low profile.However,the general difficulty in microstrip antenna design lies in its wideband el...Microstrip antennas are of significant interest and extensively utilized in communication systems because of their unique low profile.However,the general difficulty in microstrip antenna design lies in its wideband electromagnetic radiation within a low-profile structure.To enhance the bandwidth,superposing the fundamental mode and other high-order modes is the most common method,but this occupies a larger footprint than regular narrow-band modes.Here,as a counterintuitive way to broaden the bandwidth,a wideband miniaturized microstrip antenna is proposed by using two high-order modes.The avoidance of the fundamental mode allows for footprint miniaturization without decreasing the bandwidth,providing a different but feasible design strategy for wideband microstrip antennas.Compared with other microstrip antennas at the same profile,the proposed antenna achieves wider bandwidth and a smaller footprint.The experimental result shows a bandwidth of 4.81–6.01 GHz is achieved with a volume of 0.47×0.47×0.043 λ_(0)^(3),whereλ0 represents the in-vacuum wavelength at the center frequency.Therefore,the proposed design provides an effective solution to the intrinsic contradiction between wideband electromagnetic radiation and compact antenna dimensions,not only in a low profile but in a small footprint,contributing to the fundamental development of microstrip antennas.展开更多
A novel broadband metasurface (MTS) antenna array with high front-to-back ratio (FBR) is proposed for 28 GHz millimeter-wave applications. With slot pairs loaded on patch cells, an aperturecoupled slotted-mushroom MTS...A novel broadband metasurface (MTS) antenna array with high front-to-back ratio (FBR) is proposed for 28 GHz millimeter-wave applications. With slot pairs loaded on patch cells, an aperturecoupled slotted-mushroom MTS antenna is designed to obtain broadband radiation characteristicswith a compact size. To suppress the backward radiation of this antenna, the printed ridge gapwaveguide (PRGW) technology with a perfect magnetic conductor (PMC) shielding made ofmushroom unit-cells underneath the microstrip feeding line is applied. On this basis, a 4×4 MTSantenna array with the PRGW feed network is developed. Simulated results show that the FBR canbe highly improved by over 16 dB within the entire bandwidth. To validate the design, a prototypeof the proposed antenna is fabricated. Measured results show that an FBR greater than 28 dB canbe obtained over a 24% impedance bandwidth (from 24.9 GHz to 31.7 GHz) with the reflectioncoefficient less than 10 dB. The measured antenna gain ranges from 17 dBi to 19.2 dBi and thecorresponding measured aperture efficiencies are 35% and 45.6%. The measured results alsosuggest that the proposed MTS antenna possesses -35 dB cross-polarization level and stable radiation patterns. In addition, the proposed antenna remains a very low profile of 1.7 mm (0.17λ_(0) at28 GHz). All the achieved features indicate that the proposed MTS antenna is an importantcandidate for B5G and 6G wireless communication.展开更多
基金supported by the National Natural Science Foundation of China under Grant No.62101103.
文摘Against the backdrop of electromagnetic space integration,the radio system of equipment platforms,such as next-generation aircraft,must possess multifunctional integration and electromagnetic stealth performance.Meanwhile,the equipment platforms need to evolve towards flat structures.These requirements pose significant technical challenges for antenna system design.The antenna must possess ultra-wideband to facilitate multi-function integration through the use of continuous radio frequency synthetic aperture.In order to ensure good aerodynamics of the flat airborne platform,it is required to implement conformal design,while the ultra-low profile is the greatest challenge in conformal design.Against this background,this work proposes a novel airborne tightly coupled antenna with ultra-low profile,ultra-wideband,and vertical-polarized omnidirectional radiation.The antenna unit utilizes a long slot structure and implements circular conformal design,where the resistive frequency selection surface is used to expand the operating bandwidth.This antenna has a profile height of only 0.047 times the low-frequency wavelength.Simulation and measurement results show that it achieves an impedance bandwidth of nearly 12∶1 with omnidirectional beam coverage,which meets the requirements of multifunctional future airborne antennas.
基金supported in part by the National Key Research and Development Program of China(2017YFA0700201,2017YFA0700202,and 2017YFA0700203)the National Natural Science Foundation of China(61631007,61571117,61138001,61371035,61722106,61731010,11227904,and 62171124)+1 种基金the 111 Project(111-2-05)the Scientific Research Foundation of Graduate School of Southeast University(YBYP2119)。
文摘Inspired by the design philosophy of information metasurfaces based on the digital coding concept,a planar 4-bit reconfigurable antenna array with low profile of 0.15λ0(whereλ0is the free-space wavelength)is presented.The array is based on a digital coding radiation element consisting of a 1-bit magnetoelectric(ME)dipole and a miniaturized reflection-type phase shifter(RTPS).The proposed 1-bit ME dipole can provide two digital states of"0"and"1"(with 0°and 180°phase responses)over a wide frequency band by individually exciting its two symmetrical feeding ports.The designed RTPS is able to realize a relative phase shift of 173°.By digitally quantizing its phase in the range of 157.5°,additional eight digital states at intervals of 22.5°are obtained.To achieve low sidelobe levels,a 1:16 power divider based on the Taylor line source method is employed to feed the array,A prototype of the proposed 4-bit antenna array has been fabricated and tested,and the experimental results are in good agreement with the simulations.Scanning beams within a±45°range were measured with a maximum realized gain of 13.4 dBi at12 GHz.The sidelobe and cross-polarization levels are below-14.3 and-23.0 dB,respectively.Furthermore,the beam pointing error is within 0.8°,and the 3 dB gain bandwidth of the broadside beam is 25%.Due to its outstanding performance,the array holds potential for significant applications in radar and wireless communication systems.
文摘To protect the driver in case of a tractor overturn,narrow-track tractors,mainly used for working under trees or in vineyards,can be equipped with a foldable roll-over protective structure(FROPS)generally consisting of a two-pillar front-mounted foldable rollbar.FROPSs have been mainly developed to offer greater mobility when working in low overhead clearance zones(CZs)and more storage options.However,many fatalities and serious injuries in Italy are due to overturn of narrow tractors with FROPS not in safety configuration.The reason lies on that lowering and raising a conventional FROPS is a time-consuming and strenuous process.After operators fold down FROPS to pass a low overhead CZ,some prefer to leave it in the folded or inoperative position,increasing the risk of a roll-over fatality.Italian Workers Compensation Authority(Inail)collects injury reports of workers covered by compulsory accident insurance.However,for agricultural sector Inail set up in 2008 a national observatory to add data and information on fatalities in agriculture covering workers,even those not Inail insured.From these data it appears that about 10 fatalities per year occur in Italy involving folded ROPS.The aim of the analysis in this article is to make a survey on the FROPS issue considering both what is required by Mother Regulation(Regulation(EU)167/2013)for new tractors and the achievable technical solutions to be applied on old tractors for reducing the misuse of FROPS.
基金National Natural Science Foundation of China(62171459)Innovative Talents Cultivate Program for Technology Innovation Team of Shaanxi Province(2024RSCXTD-08)Key Research and Development Program of Shaanxi Province(2022GD-TSLD-64)。
文摘The finding of Snell’s law for anomalous reflection enables broad applications of metasurfaces in stealth,communication,radar technology,etc.However,some unavoidable high-order modes are inherently generated due to the super lattice of this local approach,which thus causes a decrease in efficiency and a limit in the reflected angle.Here,a novel,to our knowledge,low-profile wideband reflective meta-atom shaped like a four-leaf rose is proposed to achieve a phase coverage of full 360°by varying the length of the rose leaf.Then,the genetic algorithm is adopted for the first time to encode and optimize the topology of each meta-atom on the coding metasurface to achieve two-dimensional(2D)anomalous reflection with excellent performances through an inverse design.Numerical results show that our optimized coding metasurfaces achieve a high-efficiency(≥90%)and large-angle(θ≤70°and 0°≤φ≤360°)reflection under normal incidence.For verification,far-field measurement is carried out and experimental results are consistent with the numerical ones.Our work sets up a solid platform for utilizing algorithms,especially in artificial intelligence,in the future for arbitrary 2D anomalous reflection with high efficiency and a large angle.
基金supported by the National Foundation for Innovative Research Groups of China(Grant No.51421063)
文摘This paper presents a new idea to reduce the solidity of low-pressure turbine(LPT) blade cascades,while remain the structural integrity of LPT blade.Aerodynamic performance of a low solidity LPT cascade was improved by increasing blade trailing edge thickness(TET).The solidity of the LPT cascade blade can be reduced by about12.5% through increasing the TET of the blade without a significant drop in energy efficiency.For the low solidity LPT cascade,increasing the TET can decrease energy loss by 23.30% and increase the flow turning angle by1.86% for Reynolds number(Re) of 25,000 and freestream turbulence intensities(FSTT) of 2.35%.The flow control mechanism governing behavior around the trailing edge of an LPT cascade is also presented.The results show that appropriate TET is important for the optimal design of high-lift load LPT blade cascades.
基金This work is supported by National Natural Science Foundation of China under Grant 61801348State Key Laboratory of MillimeterWaves under contract K202031。
文摘A low-profile cylindrical dielectric resonator antenna(CDRA)with enhanced impedance bandwidth is proposed via sharing a single triple-mode dielectric resonator.Initially,the resonant frequencies of TM01d and TM02d modes of a conventional CDRA are maintained far away from each other under central probe feed.Next,a circular disk with an annular ring is loaded around the conventional CDRA,aiming to excite an additional mode between these dual modes.The electric fields demon-strate that the previous TM_(02δ) mode is transformed into the TM03d mode for the modified CDRA,and an additional TM_(02δ) mode is successfully excited between the TM_(01δ) and TM_(03δ) modes.As a result,the resonant frequencies of these three radiative modes are reallocated in proximity to each other,thus achieving the desired bandwidth enhancement.In addition,considering the small input impedance of the CDRA,a microstrip feeding line is introduced underneath the central probe for good impedance matching.With these arrangements,the resultant antenna can generate an extended bandwidth under simultaneous radiation of TM_(01δ),TM_(02δ),and TM_(03δ) modes.Finally,the proposed CDRA is designed,fabricated,and measured to validate the predicted per-formance.The simulated and measured results show that the impedance bandwidth(|S11|<-10 dB of the antenna is dramatically extended from 8%to about 62%(2.835.36 GHz),while keeping a stable conical radiation pattern.In particular,a low profile property of about 0.15 free space wavelength is achieved as well.
基金supported by the National Natural Science Foundation of China(Grant Nos.U22B2016 and 62022045)the National Key Research and Development Program of China(Grant No.2021YFA0716600)the Shenzhen Science and Technology Program(Grant No.JSGG20210802153800002).
文摘Microstrip antennas are of significant interest and extensively utilized in communication systems because of their unique low profile.However,the general difficulty in microstrip antenna design lies in its wideband electromagnetic radiation within a low-profile structure.To enhance the bandwidth,superposing the fundamental mode and other high-order modes is the most common method,but this occupies a larger footprint than regular narrow-band modes.Here,as a counterintuitive way to broaden the bandwidth,a wideband miniaturized microstrip antenna is proposed by using two high-order modes.The avoidance of the fundamental mode allows for footprint miniaturization without decreasing the bandwidth,providing a different but feasible design strategy for wideband microstrip antennas.Compared with other microstrip antennas at the same profile,the proposed antenna achieves wider bandwidth and a smaller footprint.The experimental result shows a bandwidth of 4.81–6.01 GHz is achieved with a volume of 0.47×0.47×0.043 λ_(0)^(3),whereλ0 represents the in-vacuum wavelength at the center frequency.Therefore,the proposed design provides an effective solution to the intrinsic contradiction between wideband electromagnetic radiation and compact antenna dimensions,not only in a low profile but in a small footprint,contributing to the fundamental development of microstrip antennas.
基金National Natural Science Foundation of China(62288101,62001342)National Key Research and Development Program of China(2021YFA1401001)+1 种基金Key Research and Development Program of Shaanxi(2021TD-07)Fundamental Research Funds for the Central Universities(20103224952).
文摘A novel broadband metasurface (MTS) antenna array with high front-to-back ratio (FBR) is proposed for 28 GHz millimeter-wave applications. With slot pairs loaded on patch cells, an aperturecoupled slotted-mushroom MTS antenna is designed to obtain broadband radiation characteristicswith a compact size. To suppress the backward radiation of this antenna, the printed ridge gapwaveguide (PRGW) technology with a perfect magnetic conductor (PMC) shielding made ofmushroom unit-cells underneath the microstrip feeding line is applied. On this basis, a 4×4 MTSantenna array with the PRGW feed network is developed. Simulated results show that the FBR canbe highly improved by over 16 dB within the entire bandwidth. To validate the design, a prototypeof the proposed antenna is fabricated. Measured results show that an FBR greater than 28 dB canbe obtained over a 24% impedance bandwidth (from 24.9 GHz to 31.7 GHz) with the reflectioncoefficient less than 10 dB. The measured antenna gain ranges from 17 dBi to 19.2 dBi and thecorresponding measured aperture efficiencies are 35% and 45.6%. The measured results alsosuggest that the proposed MTS antenna possesses -35 dB cross-polarization level and stable radiation patterns. In addition, the proposed antenna remains a very low profile of 1.7 mm (0.17λ_(0) at28 GHz). All the achieved features indicate that the proposed MTS antenna is an importantcandidate for B5G and 6G wireless communication.
