Showing papers by "Qiusheng Li published in 2022"

Switchable tri-function terahertz metasurface based on polarization vanadium dioxide and photosensitive silicon.

Abstract: A terahertz switchable metasurface with the function of absorption and polarization conversion is proposed. It consists of metal pattern layer - dielectric layer - VO2 layer - dielectric layer - metal pattern layer, and the photosensitive silicon is embedded in the metal pattern. When VO2 is in insulated state, the metasurface behaves as a linear polarization converter. The polarization conversion rate (PCR) is more than 90% at two frequency bands of 1.64 THz ∼ 1.91 THz and 2.35 THz ∼ 2.75 THz. The polarization converter has good asymmetric transmission ability. Moreover, the polarization conversion performance can be dynamically controlled by changing the conductivity of the photosensitive silicon. When VO2 is in metallic state, the metasurface becomes a terahertz bidirectional absorber, which exhibits different absorption properties under TE and TM waves with the maximum absorptance reaching to 100%. In addition, the absorption of TE and TM terahertz waves can be controlled at the specific frequency by changing the conductivity of photosensitive silicon. We also explore the application of dynamic control of polarization waves in the near-field image display.

A Review: The Functional Materials-Assisted Terahertz Metamaterial Absorbers and Polarization Converters

Abstract: When metamaterial structures meet functional materials, what will happen? The recent rise of the combination of metamaterial structures and functional materials opens new opportunities for dynamic manipulation of terahertz wave. The optical responses of functional materials are greatly improved based on the highly-localized structures in metamaterials, and the properties of metamaterials can in turn be manipulated in a wide dynamic range based on the external stimulation. In the topical review, we summarize the recent progress of the functional materials-based metamaterial structures for flexible control of the terahertz absorption and polarization conversion. The reviewed devices include but are not limited to terahertz metamaterial absorbers with different characteristics, polarization converters, wave plates, and so on. We review the dynamical tunable metamaterial structures based on the combination with functional materials such as graphene, vanadium dioxide (VO2) and Dirac semimetal (DSM) under various external stimulation. The faced challenges and future prospects of the related researches will also be discussed in the end.

Terahertz Metamaterial Sensor With Ultra-High Sensitivity and Tunability Based on Photosensitive Semiconductor GaAs

Abstract: We proposed and demonstrated an ultra-high sensitive refractive index metamaterial sensor within terahertz region. The sensor consists of a gallium arsenide (GaAs) structure on the top, aluminum in the middle, and a polyimide as the bottom substrate. The simulation results show that such sensor has an absorption peak at 2.0 THz with the Q-factor up to 444. The sensor is very sensitive to the change of the refractive index (RI) of the surrounding medium. The metamaterial sensor with optimized structure has a sensitivity of 1.762 THz/RIU and a figure of merit (FoM) value of 392 RIU−1, respectively. Meanwhile, both the absorption peak position and intensity of such metamaterial sensor could be adjustable. The proposed terahertz metamaterial sensor with such high sensitivity and easily tunable properties has broad application prospects in research fields including biomedical sensing, disease diagnosis, and also trace detection of hazardous substances.

Crustal Structure and Anisotropy in the Lower Yangtze Region and its Metallogenic Implications

Abstract: In this study, we performed receiver function profiling and fitted harmonic functions to the arrival time variations of Pms phases to calculate the crustal seismic anisotropy with delay time and fast polarization direction, using broadband seismic data obtained from 55 temporary stations in two linear profiles and 39 stations in the Lower Yangtze and adjacent region. Moreover, we determined the crustal thickness and Poisson’s ratio using a novel H-κ-c stacking method. Our results revealed that the Middle-Lower Yangtze Metallogenic Belt and the north east section of the Qinzhou-Hangzhou Metallogenic Belt are characterized by Moho upliftment (<32 km), a relatively high Poisson’s ratio (>0.26), local lithospheric thinning (<70 km), and a pattern of deep faults that connect the crust and asthenosphere and serve as conduits for magma upwelling. The NE-SW fast polarization direction was consistent with the SKS splitting results, and the average delay time was 0.45 s. Moreover, underplating of deep magma and upwelling along the weak zone caused local Moho uplift and ductile shear of the lower crust, resulting in the directional arrangement of amphibole and other minerals, which may be the controlling mechanism for the crustal anisotropy in the study area. The variations in crustal structure and anisotropy characteristics indicated that in the context of the northeastern Paleo-Pacific plate subduction, the existence of weak lithospheric zones and the northeastern asthenospheric flow are important conditions for metal supernormal enrichment in the Lower Yangtze region.

Modal Identification of Civil Structures via Stochastic Subspace Algorithm with Monte Carlo–Based Stabilization Diagram

Abstract: The stochastic subspace algorithm is one of the most widely used structural identification techniques, which is generally involved with the stabilization diagram for estimating modal parameters. However, the conventional stabilization diagram has an inherent problem: some spurious modes may be identified as stable results, resulting in adverse effects on structural modal identification. To address this critical issue, this paper proposes an improved stochastic subspace algorithm involving a Monte Carlo–based stabilization diagram. Through a numerical simulation study, the good performance of the Monte Carlo–based stabilization diagram for discriminating the poles denoting the physical modes from those representing spurious modes is demonstrated. The numerical simulation results show that the proposed method can estimate structural modal parameters with high accuracy and robustness. Moreover, the proposed method is applied to field measurements on a 600-m-high skyscraper during Super Typhoon Mangkhut, and the results verify the applicability and effectiveness of the proposed method to field measurements. This paper aims to provide an effective tool for accurate estimation of modal parameters of civil structures.

Switchable terahertz broadband absorption and linear-to-circular polarization conversion

Abstract: We proposed a switchable bifunctional metasurface for broadband absorber and linear-to-circular polarization converter (LTCPC) in terahertz regime. When vanadium dioxide (VO2) is in the metallic state, the designed metasurface acts as a broadband terahertz absorber. The results demonstrate that the absorptance is above 90% and the bandwidth ratio is 68.6% from 0.981 to 2.011 THz. When VO2 is in the insulated state, the proposed structure behaves as an LTCPC with ellipticities 1 and −1 in frequency bands of 0.391∼0.517 and 0.673∼2.363 THz, respectively. The axis ratio is lower than 3 dB. The designed metasurface provides a new method for designing multifunctional terahertz devices.

Horizontal displacement estimation of high-rise structures by fusing strain and acceleration measurements

Abstract: Monitoring of horizontal displacement is essential for structural health monitoring of high-rise structures. This paper proposes a new technique for estimating the horizontal displacement using fusion measurements including strain and acceleration for high-rise structures. The quasi-static component of structural displacement is first derived from the measured longitudinal strains based on the classical beam theory . The quasi-static displacement is then combined with the resonant displacement determined based on the measured acceleration via a finite impulse response filtering approach to obtain the total horizontal displacement. The effectiveness of the proposed technique is examined through numerical studies, in which two cantilever beams with different sectional shapes are used to verify that the proposed technique can provide accurate estimation of horizontal displacements under different noise levels contained in signals and number of measurement points. Then, a field measurement validation study on a 600 m high skyscraper is presented to demonstrate the applicability and accuracy of the proposed technique for horizontal displacement estimation of high-rise buildings under typhoon conditions. • Propose a horizontal displacement estimation technique fusing acceleration and strain measurements for high-rise structures. • Examine the effectiveness and accuracy of the proposed technique through numerical validation studies. • Verify the performance of the proposed technique based structural responses of a skyscraper under typhoon condition.

Control performance of active tuned mass damper for mitigating wind-induced vibrations of a 600-m-tall skyscraper

Abstract: Based on the field measurements on a 600-m-tall skyscraper equiped with an active tuned mass damper (ATMD) system, this paper investigates the control performance of the world's largest ATMD system to suppress the building vibrations. On-site forced vibration tests on the skyscraper were first conducted and the results showed that the ATMD system can increase the damping ratios of the fundamental sway modes up to about 11 times. Accordingly, ambient vibration tests on the building during Super Typhoon Hato were carried out, and the measured building acceleration responses showed that the ATMD system can effectively suppress the wind-induced vibrations of the skyscraper. Moreover, the structural damping ratios of the building with and without the operation of the ATMD system were identified, which showed that the ATMD system can significantly boost the damping ratios of the fundamental sway modes of the building for suppressing wind-induced vibrations, while it had limited effects on higher modal responses. The paper aims to provide useful information for the design of active vibration control systems and the wind-resistant design of high-rise buildings.

Combination regulation of terahertz OAM vortex beams on multi-bit metasurface

Abstract: High efficiency terahertz orbital angular momentum (OAM) vortex beam manipulation is of crucial importance for ultra large capacity wireless communication in terahertz frequencies region. We present a silicon-based multi-bit encoded metasurface structure based on convolution and addition theorem to generate flexible regulation of OAM multiple combinations such as vortex beam and beam splitting combination, vortex beam splitting, deflected beam and vortex beam combination. The proposed metasurfaces is composed of periodic array of silicon pillar with quadrangular ridge on top of a metal plate substrate. The advantage of this scheme in producing vortex beam is its simple structure, flexible design and controls to arbitrary presented directions easily. This work provides a new approach to realize powerful and flexible adjustment of terahertz wave.

Terahertz vortex beam generator carrying orbital angular momentum in both transmission and reflection spaces.

Abstract: Vortex beam generators carrying orbital angular momentum (OAM) with both transmission and reflection modes has broad application prospects in full-space high data capacity communication and orbital angular momentum multiplexing systems. In this work, we proposed a vanadium dioxide (VO2) assisted metasurface to independently produce and manipulate focused vortex transmission-reflection modes with different number of beams and focal lengths under right-handed circular polarized (RCP) wave incidence. The proposed metasurface generates the diagonal vortex beams, four vortex beams, and focused vortex beam for transmission mode at 1.26THz and reflection mode at 1.06THz by changing phase state of the VO2. Our work may find many potential applications in future high data capacity information multiplexing communication systems.

Simultaneous and independent regulation of circularly polarized terahertz wave based on metasurface.

Abstract: A single metasurface-based device possessing multiple functionalities is highly desirable for terahertz technology system. In this paper, we design a reflective metasurface to generate switchable vortex beams carrying orbital angular momentum (OAM), focusing beams, focusing beams with arbitrary positions, and vortex beams with arbitrary topological charges in the terahertz region. By combining the spin decoupling principle and the phase addition theorem, the superposition states of OAM and focusing beams with arbitrary positions can be independent manipulated under right-handed and left-handed circularly polarized (LCP/RCP) waves illumination. Such a diversified functionalities device provides a promising application in the field of terahertz communication and terahertz super-resolution imaging.

Modal Identification Technologies for High-Rise Buildings Under Non-Stationary Excitations

Abstract: For high-rise buildings subjected to typhoon or earthquake actions, the excitations are likely non-stationary, which inevitably violates the stationary assumption that is generally adopted by conventional modal identification methods. Under such a condition, conventional modal identification methods may not be applicable, and their performances need to be evaluated. To this end, the performances of seven widely used modal identification algorithms for structural modal estimation under non-stationary excitations are evaluated via a numerical simulation study. Then, three methods with good performance are selected to evaluate their applicability and accuracy for field measurements involving non-stationary excitations. From the comparative study, a time–frequency domain method with the best performance among these seven methods is employed to investigate the structural dynamic properties of a 509-m-tall skyscraper under typhoon and earthquake excitations. Based on the reliable modal estimates, the relationships between the modal properties with response amplitude and environmental temperature are presented and discussed. This paper aims to identify the effective methods for accurate estimation of structural modal parameters based on non-stationary structural responses and investigate the structural dynamic properties of high-rise buildings under typhoon and earthquake excitations.

Transmission/reflection/absorption individually control multifunctional metasurfaces

Abstract: We propose a metasurface based on hybrid phase change materials GeTe and vanadium dioxide (VO 2 ), which can manipulate the transmission /reflection /absorption of terahertz waves independently. By changing the external temperature from 25°C to 160°C, the function of this structure can be dramatically changed. When VO 2 is in a dielectric state (i.e. 25°C), the designed structure behaves as a transmission-mode terahertz vortex beams manipulator. When VO 2 is in a dielectric state (i.e. 68°C), the proposed structure serves as a reflection-mode terahertz vortex beams controller. When GeTe is in crystalline state (i.e. 160°C), the designed structure becomes as a terahertz perfect absorber at a frequency of 1.98THz within the incident angle of 30°. The proposed structure provides a new method toward the use of multifunctional terahertz devices for their potential in applications including terahertz wireless communication and detection.

Modal identification of high-rise buildings under earthquake excitations via an improved subspace methodology

Abstract: The subspace state-space system identification method has drawn extensive attention in structural modal identification, which is generally involved with the stabilization diagram for estimating structural modal parameters. However, the conventional stabilization diagram has an inherent problem, i.e., some spurious modes may be identified as stable results, leading to the adverse effect on structural modal identification. To address this issue, this paper proposes an improved subspace algorithm, in which a Monte Carlo-based stabilization diagram is involved. The performance of the Monte Carlo-based stabilization diagram for discriminating the poles denoting the physical modes from those representing spurious modes is demonstrated through a numerical study. The simulation results further prove that the proposed method can accurately estimate the time-varying structural modal parameters. Moreover, the proposed method is applied to field measurements on a 218-m-tall building during the 1994 Northridge earthquake event, and the identified results verify the applicability and effectiveness of the proposed method in field measurements. This paper aims to provide an effective tool for modal identification of high-rise buildings under earthquake excitations.

Switchable vortex beam polarization states terahertz multi-layer metasurface

Abstract: We proposed a switchable vortex beam polarization states terahertz multi-layer metasurface, which consists of three-layer elliptical metal crosses, four-layer dielectrics and two-layer hollow metal circles alternately superimposed. Under the normal incidence of left circularly polarized (LCP) and right circularly polarized (RCP) waves, the proposed structure realizes three independent control functions including focusing and vortex beam, vortex beam with different topological charges and polarization states switching, and azimuth switching of two vortex beams with different polarization states. The results show that the proposed metasurface provides a new idea for multifunctional terahertz wave modulation devices.

Dual functional terahertz metasurface based on vanadium dioxide and graphene

Abstract: A dual functional terahertz metasurface based on VO2 and graphene is proposed in this paper. It consists of gold layer embedded with VO2 patches, SiO2 spacer layer, VO2 layer, graphene and SiO2 spacer substrate. When the bottom VO2 is in metallic state, the designed metasurface can achieve absorption function. As the top VO2 patches are metallic state, the proposed metasurface can be used as single band absorber with terahertz absorptance of 99.7 % at 0.736 THz. When the top VO2 patches are in insulating state, the designed structure behaves as dual band absorber with the absorptance of 98.9 % at 0.894 THz and 99.9 % at 1.408 THz. In addition, the absorber is polarization insensitive and keeps good performance at large incident angle. When the bottom VO2 is in insulated state, the metasurface serves as electromagnetically induced transparency. The transparent window can be dynamically regulated by controlling the chemical potential of graphene. The proposed metasurface exhibits the advantages of terahertz absorption, electromagnetic induced transparency and dynamic control, which provides more options for the design of terahertz devices in the future.

Terahertz device utilizing a transmissive geometric metasurface.

Abstract: Due to potential applications in next generation high-capacity wireless communication systems, generating and controlling vortex beams carrying orbital angular momentum (OAM) has received considerable attention. In this work, a scheme is proposed to generate two/four splitting vortex beams and focusing vortex beams with different topological charges under left circularly polarized and right circularly polarized terahertz waves under incidence. The meta-unit cell consists of a two-flying-fish-shaped patterned metallic top layer and an identical metallic patterned bottom layer separated by a silica layer. Full-wave simulation results agree well with that of calculation predictions. The proposed terahertz metasurface-based devices are able to carry different OAM modes and can abruptly manipulate during propagation, which indicates that such metasurface-based devices may have promising applications in terahertz wireless communication links in the future.

Bidirectional Terahertz Vortex Beam Regulator

Abstract: Most of the reported vortex beam generators with orbital angular momentum (OAM) in the terahertz region only operate in either the reflection mode or the transmission mode, which greatly limits the integration and application in terahertz technology systems. Herein, we propose a full-space vortex beam regulator at two different frequencies. By changing the VO2 phase transition state, the transmission and reflection mode OAM beams can be flexibly controlled by a single metasurface. For the transmission mode, the proposed structure realizes an OAM beam at the topological charges of l = 1 and 2 at 0.6 THz and 1.4 THz. For the reflection mode, our structure generates an OAM beam at the topological charges of l = 1 and 2 at 0.9 THz and 1.5 THz. Based on the superposition theorem and convolution operation principle, the regulation of an OAM vortex beam with a specific deflection angle and a symmetrical deflection OAM vortex beam are realized. The designed metasurface integrates multiple transmitted and reflected vortex beam functions in full space and has potential application in different terahertz systems.

The Thinnest Crust in South China Associated With the Cretaceous Lithospheric Extension: Evidence From SINOPROBE Seismic Reflection Profiling

Abstract: Long‐standing debates exist over the mechanism of continental lithospheric extension and, more specifically, over the strain distribution across the lithosphere in intraplate settings. The Cretaceous extensional system in South China extends up to ∼800 km inboard of the Paleo‐Pacific convergent margin and enables investigation of the mechanism(s) of intraplate lithospheric extension. Here we use high‐resolution seismic reflection data to image the crustal and upper‐mantle architecture of the central segment of the extensional system. We identify a compositionally stratified upper lithosphere that has undergone depth‐dependent extension, expressed by heterogeneous normal faulting in the upper crust, widely distributed ductile stretching in the lower crust, mantle influx into the crust, a broadly smooth Moho with localized uplift, and mantle shear‐zone generation. We detect, beneath the center of the Ganzhou Rift, the thinnest crust (28–30 km thick) in South China. It spatially correlates with the locus of strong lithospheric thinning and asthenospheric upwelling. We suggest that the generation of the thinnest crust was assisted by lower‐crustal ductile stretching, mantle shearing, and exhumation during depth‐dependent extension. Our study provides insights into the partitioning of depth‐dependent extensional strain into an intraplate stratified lithosphere and the feedback between crustal and mantle processes that shaped the thinnest crust at a position ∼300 km inboard of the convergent margin during continental extension.

Multifunctional reflection type anisotropic metasurfaces in terahertz band

Abstract: Based on the convolution and superposition theorem, we propose a reflective anisotropic metasurface to realize the functions of deflection and superposition of vortex beams, bifocal focusing, and focusing vortex beam. At frequency of 1.04THz, two deflection vortex beams with topological charges of ( l =-1 and l =+2) and ( l =+1 and l =-2) are generated under x - and y -polarized terahertz wave incidence, respectively. At focal plane, 1200µm from the top layer of the proposed metasurface, one can see that the bifocal focusing along y -axis and x -axis are produced under x - and y -polarized terahertz wave incidence, respectively. Similarly, focusing vortex beams with l =+1 and l =-2 are realized under x - and y -polarized terahertz wave incidence, respectively. The designed metasurface can flexibly manipulate terahertz wave under different polarization waves incidence and has potential application prospects in fields of terahertz communication.

Tunable anisotropic metasurface by utilizing phase change material in terahertz range

Abstract: Abstract. Due to the capability of achieving versatile control of differently polarized electromagnetic waves, anisotropic metasurfaces have attracted extensive attentions. To manipulate terahertz waves flexibly, we propose a tunable anisotropic metasurface based on phase change material vanadium dioxide (VO2). It is composed of a gold bottom layer deposited on the back of polyimide dielectric layer and a gold patch located on the front of the polyimide dielectric substrate. When VO2 is in the insulating state, the predesigned metasurface produces diversified functions, including terahertz beam splitting, deviation focusing, and multivortex beam under different polarization terahertz wave incidence. When VO2 becomes a metallic state, the proposed metasurface changes the number of terahertz beams, the shape of vortex beams, and the focusing effect. This scheme provides an innovative idea for the dynamic regulation of the terahertz wave in future terahertz technology systems.