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  • 251. Jin, Yi
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    IMPEDANCE-MATCHED MULTILAYERED STRUCTURE CONTAINING A ZERO-PERMITTIVITY MATERIAL FOR SPATIAL FILTERING2008Ingår i: Journal of nonlinear optical physics and materials, ISSN 0218-8635, Vol. 17, nr 3, s. 349-355Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Based on the effective medium theory, a multilayered spatial filter is constructed with an ultralow-permittivity material and a typical dielectric. Besides the special property of an ultralow refractive index, the designed periodic structure is impedance-matched to free space, regardless of the total thickness. The present spatial filter works well even when moderate loss exists.

  • 252. Jin, Yi
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Negative refraction of complex lattices of dielectric cylinders2007Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 360, nr 3, s. 461-466Artikel i tidskrift (Refereegranskat)
  • 253. Jin, Yi
    et al.
    Xiao, Sanshui
    Mortensen, N. Asger
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Arbitrarily thin metamaterial structure for perfect absorption and giant magnification2011Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, nr 12, s. 11114-11119Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In our common understanding, for strong absorption or amplification in a slab structure, the desire of reducing the slab thickness seems contradictory to the condition of small loss or gain. In this paper, this common understanding is challenged. It is shown that an arbitrarily thin metamaterial layer can perfectly absorb or giantly amplify an incident plane wave at a critical angle when the real parts of the permittivity and permeability of the metamaterial are zero while the absolute imaginary parts can be arbitrarily small. The metamaterial layer needs a totally reflective substrate for perfect absorption, while this is not required for giant magnification. Detailed analysis for the existence of the critical angle and physical explanation for these abnormal phenomena are given.

  • 254.
    Jin, Yi
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhang, Pu
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Abnormal enhancement of electric field inside a thin permittivity-near-zero object in free space2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 7, s. 075118-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is found that the electric field can be enhanced strongly inside a permittivity-near-zero object in free space, when the transverse cross section of the object is small and the length along the propagation direction of the incident wave is large enough as compared with the wavelength. The physical mechanism is explained in details. The incident electromagnetic energy can only flow almost normally through the outer surface into or out of the permittivity-near-zero object, which leads to large energy stream density and then strong electric field inside the object. Meanwhile, the magnetic field inside the permittivity-near-zero object may be smaller than that of the incident wave, which is also helpful for enhancing the electric field. Two permittivity-near-zero objects of simple shapes, namely, a thin cylindrical shell and a long thin rectangular bar, are chosen for numerical illustration. The enhancement of the electric field becomes stronger when the permittivity-near-zero object becomes thinner. The physical mechanism of the field enhancement is completely different from the plasmonic resonance enhancement at a metal surface.

  • 255.
    Jin, Yi
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhang, Pu
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Squeezing electromagnetic energy with a dielectric split ring inside a permeability-near-zero metamaterial2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An electromagnetic energy squeezing mechanism is proposed based on the special properties of permeability-near-zero metamaterials. It is found that nearly no energy stream can enter a simply connected conventional dielectric material positioned inside a permeability-near-zero material. When the dielectric domain is shaped as a split ring (with a gap opened) surrounding a source, the electromagnetic energy generated by the source is forced to propagate through the gap. When the gap is narrow, the energy stream density becomes very large and makes the magnetic field enhanced drastically in the gap. The narrow gap can be long and bended. This provides us a method to obtain strong magnetic field without using resonance enhancement.

  • 256. Khan, S. N.
    et al.
    Hu, J.
    Xiong, J.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Circular fractal monopole antenna based on descartes circle theorem for uwb application2008Ingår i: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 50, nr 6, s. 1605-1608Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An apollonian shaped ultra-wideband circular monopole antenna based oil descartes circle theorem is presented. Different self similar geometries front DCT are analyzed and optmized for UWB applications. The proposed design is slightly modified to ensure all overall smooth current distribution limited by the Junction point nature of the fractal geometries. The experimental results are compared with conventional circular disk monopole (and annular monopole antenna. The measured return loss of the proposed design below - 10 dB is from 2.4 to over 40 GHz and its radiation pattern is omni-directional compared with circular disk and annular antennas in most of its impedance bandwidth. Moreover due to the fractal shape, the proposed design has less weight and wind loading effect.

  • 257. Khan, S. N.
    et al.
    Shual, Z.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    LOW PROFILE AND COMPACT SIZE COPLANAR UWB ANTENNA WORKING FROM 2.8 GHz TO OVER 40 GHz2009Ingår i: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 51, nr 2, s. 408-411Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A square monopole coplanar antenna with a circular base is proposed for ultra wideband (UWB) communications. The design parameters are analyzed and optimized to obtain a good performance and the measured return loss below -10 dB is front 2.8 to over 40 GHz. The proposed antenna has advantages of low profile, small size, UWB and omni-directional pattern.

  • 258. Khan, S. N.
    et al.
    Xiong, J.
    He, Sailing
    Low profile and small size frequency notched planar monopole antenna from 3.5 to 23.64 ghz2008Ingår i: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 50, nr 1, s. 235-236Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A small size and low profile microstrip fed frequency notched planar monopole ultra wideband (UWB) antenna with an arc shaped slot etched on a circular disk is proposed. The effect of different dimensions of the slotted arc are analyzed and optimized to obtain simultaneously the UWB and the band rejected performance. The return loss from (3.5-23.64 GHz) along with a notched frequency band (5.23-5.8 GHz) and quasi omni-directional radiation pattern is observed.

  • 259. Khan, S. N.
    et al.
    Xiong, J.
    Hu, J.
    He, Sailing
    A modified coplanar monopole antenna of circular disk with an ultra wide bandwidth from 2.28 similar to 38.2 GHz2008Ingår i: Journal Electromagnetic Waves and Applications, ISSN 0920-5071, E-ISSN 1569-3937, Vol. 22, nr 4, s. 593-598Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple coplanar monopole antenna of circular disk is proposed for ultra-wideband (UWB) applications. Coplanar ground plane is slightly modified with an arc-shaped cut, so that an improved impedance bandwidth, especially at the higher frequencies is achieved. The measured return loss from 2.28 similar to 38.2GHz is below -10dB and the measured radiation pattern is quasi omni-directional.

  • 260. Khan, S N
    et al.
    Yao, J
    Shuai, Z
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Modified square uwb monopole antenna for improved impedance bandwidth2008Ingår i: Journal Electromagnetic Waves and Applications, ISSN 0920-5071, E-ISSN 1569-3937, Vol. 22, nr 14-15, s. 1883-1888Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Square monopole is modified to improve the impedance bandwidth. The modified square monopole has a step-generated circular base. The measured return loss below -10 dB is from 2.42 GHz to over 20GHz and good omnidirectional radiation pattern is also achieved.

  • 261. Khan, S. N.
    et al.
    Zhang, Q. L.
    He, Sailing
    LEFT HANDED MICROSTRIP TRANSMISSION LINE LOADED WITH COMBINATION OF SPLIT RING RESONATOR AND COMPLEMENTARY-SRR2008Ingår i: Journal Electromagnetic Waves and Applications, ISSN 0920-5071, E-ISSN 1569-3937, Vol. 22, nr 13, s. 1857-1863Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An approach to realize left-handedness in microstrip transmission line by simultaneously loading it with split ring resonator and complementary split ring resonator is proposed. A transmission line individually loaded with either with SRR (-mu) or CSRR (-epsilon) has band rejection but when simultaneously loaded has a passband near the previously rejected band due to negative values of both -mu and -epsilon. i.e., left handedness. The design is compact, low pro. le and independent of the substrate permittivity. Simulation and experimental results are also presented and the design is suitable for devices like fiters and couplers.

  • 262.
    Khan, Salman Naeem
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Dai, Daoxin
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Liu, Liu Ming
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Wosinski, Lech
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    He, Sailing
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Optimal design for a flat-top AWG demultiplexer by using a fast calculation method based on a Gaussian beam approximation2006Ingår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 262, nr 2, s. 175-179Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Passband broadening of an AWG (array waveguide grating) demultiplexer with an MMI (multimode interference) coupler connected at the end of a tapered input waveguide is considered. An explicit formula based on the field propagation of an approximate Hermit-Gaussian beam is used to calculate quickly and reliably the spectral response of the AWG demultiplexer. The widths of the input waveguide, the output waveguides and the MMI coupler are optimized. The optimal design is verified with the experimental measurement.

  • 263. Kou, Pengfei
    et al.
    Yang, Liu
    Chang, Cheng
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES).
    Improved Flexible Transparent Conductive Electrodes based on Silver Nanowire Networks by a Simple Sunlight Illumination Approach2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 42052Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Silver nanowire (Ag NW) networks have attracted wide attention as transparent electrodes for emerging flexible optoelectronics. However, the sheet resistance is greatly limited by large wire-to-wire contact resistances. Here, we propose a simple sunlight illumination approach to remarkably improve their electrical conductivity without any significant degradation of the light transmittance. Because the power density is extremely low (0.1 W/cm(2), 1-Sun), only slight welding between Ag NWs has been observed. Despite this, a sheet resistance of <20 Omega/sq and transmittance of similar to 87% at wavelength of 550 nm as well as excellent mechanical flexibility have still been achieved for Ag NW networks after sunlight illumination for 1 hour or longer, which are significant upgrades over those of ITO. Slight plasmonic welding together with the associated self-limiting effect has been investigated by numerical simulations and further verified experimentally through varied solar concentrations. Due to the reduced resistance, high-performance transparent film heaters as well as efficient defrosters have been demonstrated, which are superior to the previously-reported Ag NW based film heaters. Since the sunlight is environmentally friendly and easily available, sophisticated or expensive facilities are not necessary. Our findings are particularly meaningful and show enormous potential for outdoor applications.

  • 264. Kuang, Jingguo
    et al.
    Jin, Yi
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    An open wedge cavity based on the negative refraction of a photonic crystal2006Ingår i: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 16, nr 11, s. 582-584Artikel i tidskrift (Refereegranskat)
  • 265. Lang, T. T.
    et al.
    He, J. J.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Cross-order arrayed waveguide grating design for triplexers in fiber access networks2006Ingår i: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 18, nr 01-4, s. 232-234Artikel i tidskrift (Refereegranskat)
  • 266. Lang, Tingting
    et al.
    He, Jian-Jun
    Kuang, Jing-Guo
    He, Sailing
    Birefringence compensated AWG demultiplexer with angled star couplers2007Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, nr 23, s. 15022-15028Artikel i tidskrift (Refereegranskat)
  • 267. Li, Borui
    et al.
    Sun, Fei
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Acoustic surface transformation realized by acoustic-null materials using bilayer natural materials2017Ingår i: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 10, nr 11, artikel-id 114001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a general method, known as acoustic surface transformation (AST), to design novel acoustic devices and study the realization of such devices by using naturally available materials in broadband acoustic frequencies. All devices designed by AST only need one anisotropic homogeneous acoustic-null material (ANM). We design the ANM by exploiting natural material-based metal-fluid structures and verify that by numerical simulation. Unlike traditional methods, no complicated mathematical calculations are needed. We only need to design the geometrical shapes of the input and output surfaces of the devices. The proposed method will pave a new road for future acoustic design.

  • 268. Li, Borui
    et al.
    Sun, Fei
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Reducing the dimensions of acoustic devices using anti-acoustic-null media2018Ingår i: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 11, nr 2, artikel-id 024301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An anti-acoustic-null medium (anti-ANM), a special homogeneous medium with anisotropic mass density, is designed by transformation acoustics (TA). Anti-ANM can greatly compress acoustic space along the direction of its main axis, where the size compression ratio is extremely large. This special feature can be utilized to reduce the geometric dimensions of classic acoustic devices. For example, the height of a parabolic acoustic reflector can be greatly reduced. We also design a brass-air structure on the basis of the effective medium theory to materialize the anti-ANM in a broadband frequency range. Numerical simulations verify the performance of the proposed anti-ANM.

  • 269.
    Li, Chenxi
    et al.
    Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Evans, Julian
    Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Wang, Nan
    Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Guo, Tingbiao
    Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion. Royal Inst Technol, Dept Electromagnet Engn, S-10044 Stockholm, Sweden..
    pH dependence of the chirality of nematic cellulose nanocrystals2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 11290Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cellulose nanocrystals produced by acid hydrolysis of native cellulose form a well-known chiral nematic liquid crystal phase. The mechanism involved in the formation of chirality has been the subject of a vigorous discussion. The pH and concentration dependence of the phase is studied using cellulose nanocrystal droplets within a silicon oil suspension, which allows for convenient real-time microscale manipulation of phase behaviors and properties. We demonstrate the existence of nematic phases at both low and high pH regions consistent with the Stroobants - Lekkerkerker - Odijk theory. Our results confirm electrostatic interactions play a critical role in controlling the strength of the chirality.

  • 270.
    Li, Chenxi
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China.
    Evans, Julian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China.
    Wang, Nan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China.
    Guo, Tingbiao
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China.
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China.
    Preparation and liquid crystal phase properties of discotic cellulose nanoparticles2019Ingår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, nr 18, s. 9543-9552Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the behavior of fluids with inhomogeneous structural properties is critical for many industrial and biological materials. Sulfuric acid hydrolysis of cotton with ultrasonic treatment and low-speed centrifugation during purification yields "spiky" discotic cellulose particles. Amorphous cellulose remained in solution and forms discotic units which may be nucleated by crystalline rods. Scanning electron microscope and transmission electron microscope images confirm the discotic nature of the cellulose. High speed centrifugation could recover rod-like cellulose nanocrystals from the discotic cellulose nanoparticle solution. 3.6 wt% discotic cellulose nanoparticles formed the typical nematic phase and the liquid crystal texture became more structured with increasing concentration. Our results showed that spontaneous structuring of amorphous cellulose can lead to phase behavior that cannot be achieved using just rod-like cellulose nanocrystals. Graphic abstract Mixtures containing amorphous and crystalline cellulose can form discotic cellulose nanoparticles. These solutions can form nematic phase (A), a structured columnar-like phase (B), and a glassy phase [GRAPHICS] .

  • 271.
    Li, Chenxi
    et al.
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Wang, Nan
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Guo, Tingbiao
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Evans, Julian
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Preparation of optical waveplates from cellulose nanocrystal nematics on patterned polydimethylsiloxane substrates2019Ingår i: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 9, nr 12, s. 4614-4623Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optical waveplates play an essential role in controlling polarization in various applications. We show the feasibility of facile production of optical waveplates from plant-based cellulose nanocrystal (CNC) nematics. We align CNC nematic liquid crystals doped with polyethylene glycol on periodically patterned polydimethylsiloxane substrates on large scale by shearing forces and prepare a 1/4 lambda and a 1/2 lambda CNC waveplates for 530 nm by bonding two slices of CNC nematic films with half-period displacement. The optical performance of the CNC waveplates is investigated by Mueller matrix analysis and is examined by measuring the transmission spectra of the waveplate between two polarizers, and optical extinction and birefringence of CNCs are extracted from the measured spectra. Our CNC waveplates of arbitrary phase difference are flexible and can be tailored into any desirable shape conveniently.

  • 272. Li, H.
    et al.
    Khan, S.
    Liu, J. X.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    PARAMETRIC ANALYSIS OF SIERPINSKI-LIKE FRACTAL PATCH ANTENNA FOR COMPACT AND DUAL BAND WLAN APPLICATIONS2009Ingår i: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 51, nr 1, s. 36-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Sierpinski-like fractal patch antenna with a slant strip in the first iteration is proposed in this article. The parameters of this kind of antenna are analyzed and optamized for dual WLAN application. The added slant strip provides simple probe feeding for compactness and also helps bandwidth enhancement due to multiple modes, which can be evident from current distribution. Measured return loss below,front 2.38-2.45 GHz and 5.17-5.83 GHz, coinciding well -10 dB is with dual band WLAN standard. The boresight gain and radiation pattern in different planes are also presented.

  • 273. Li, H. N.
    et al.
    He, Sailing
    Li, H. Y.
    Valence band photoemission of Yb2.75C602004Ingår i: Wuli xuebao, ISSN 1000-3290, Vol. 53, nr 1, s. 244-247Artikel i tidskrift (Refereegranskat)
  • 274. Li, H. N.
    et al.
    He, Sailing
    Zhang, H. J.
    Lu, B.
    Bao, S. N.
    Li, H. Y.
    He, P. M.
    Xu, Y. B.
    Hao, T. L.
    Electronic structure of Yb2.75C602003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 16Artikel i tidskrift (Refereegranskat)
  • 275. Li, H. N.
    et al.
    Li, H. Y.
    Wu, T. Q.
    He, Sailing
    Sun, Y. J.
    Xu, Y. B.
    Preparation and vibrational modes of C-60 center dot 2CHBr(3)2003Ingår i: Chinese Science Bulletin, ISSN 1001-6538, E-ISSN 1861-9541, Vol. 48, nr 10, s. 961-964Artikel i tidskrift (Refereegranskat)
  • 276. Li, H. N.
    et al.
    Wang, X. X.
    He, Sailing
    Ibrahim, K.
    Qian, H. J.
    Su, R.
    Zhong, J.
    Abbas, M. I.
    Hong, C. H.
    Electronic state of C-60 monolayer on Ag(111) before and after Yb intercalation2005Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 586, nr 01-3, s. 65-73Artikel i tidskrift (Refereegranskat)
  • 277. Li, H. N.
    et al.
    Wang, X. X.
    He, Sailing
    Zhang, H. J.
    Li, H. Y.
    Bao, S. N.
    Electronic structure of Yb/H-Si(111) interface2004Ingår i: Chinese Physics (Beijing), ISSN 1009-1963, E-ISSN 1741-4199, Vol. 13, nr 11, s. 1941-1946Artikel i tidskrift (Refereegranskat)
  • 278.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A compact reconfigurable antenna with pattern diversity2012Ingår i: Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE, IEEE , 2012, s. 6348776-Konferensbidrag (Refereegranskat)
    Abstract [en]

    A compact pattern reconfigurable antenna is proposed, in which the beam pattern can be switched between a monopole like radiation and a broadside radiation. Two layers and three PIN diodes are employed in the antenna. A single coaxial feed is utilized to excite both monopole mode and PIFA mode at a center frequency of 2.62 GHz. The total efficiencies of the antenna are 72% and 95% for monopole and PIFA modes, respectively. The envelope correlation coefficient calculated from the two patterns is 0.28, indicating good diversity performance of the antenna in wireless communications.

  • 279.
    Li, Hui
    et al.
    Dalian Univ Technol, Sch Informat & Commun Engn, Dalian 116024, Peoples R China..
    Lau, Buon Kiong
    Lund Univ, Dept Elect & Informat Technol, SE-22100 Lund, Sweden..
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Design of Closely Packed Pattern Reconfigurable Antenna Array for MIMO Terminals2017Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, nr 9, s. 4891-4896Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this communication, a compact pattern reconfigurable dual-antenna array is designed at 2.65 GHz for multiple-input multiple-output (MIMO) terminal applications, such as laptops. Each antenna is composed of two layers, i.e., the monopole layer and the planar inverted-F antenna (PIFA) layer. By switching the p-i-n diodes on each layer, its radiation patterns can be varied between conical and boresight patterns. Two such identical antennas are placed side by side on a common ground plane for MIMO application, providing altogether four operating modes. The center-to-center separation between the antennas is 0.25 wavelength, to keep the overall array compact. To facilitate an isolation of above 17 dB over all the modes for this compact array, two decoupling techniques based on the decoupling slits and the shielding wall are effectively combined. The envelope correlation coefficients (ECCs) of the far-field patterns in the four modes are below 0.05 in free space, and below 0.1 for most cases in the indoor and outdoor scenarios. The only exception is the monopole-PIFA mode in the outdoor scenario, but the ECC is still below 0.3 for this case. The measured efficiencies of the antennas are between -1.7 (68%) and -0.7 dB (85%) for all the modes. Therefore, good diversity and MIMO performances are expected for the proposed design.

  • 280.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lau, Buon Kiong
    Tan, Yi
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A pattern reconfigurable antenna array for multiple antenna systemsArtikel i tidskrift (Övrigt vetenskapligt)
  • 281.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lau, Buon Kiong
    Ying, Zhinong
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Decoupling of Multiple Antennas in Terminals With Chassis Excitation Using Polarization Diversity, Angle Diversity and Current Control2012Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 60, nr 12, s. 5947-5957Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Excitation of the chassis enables single-antenna terminals to achieve good bandwidth and radiation performance, due to the entire chassis being utilized as the main radiator. In contrast, the same chassis excitation phenomenon complicates the design of multiple antennas for MIMO applications, since the same characteristic mode of the chassis may be effectively excited by more than one antenna, leading to strong mutual coupling and severe MIMO performance degradation. In this paper, we introduce a design concept for MIMO antennas to mitigate the chassis-induced mutual coupling, which is especially relevant for frequency bands below 1 GHz. We illustrate the design concept on a dual-antenna terminal at 0.93 GHz, where a folded monopole at one chassis edge excites the chassis' fundamental electric dipolemode and a coupled loop at the other chassis edge excites its own fundamental magnetic dipole mode. Since the two radiationmodes are nearly orthogonal to each other, an isolation of over 30 dB is achieved. Moreover, we show that the antenna system can be conveniently modified for multiband operation, such as in the 900/1800/2600MHz bands. Furthermore, by controlling the phase of the feed current on the folded monopole, the two antennas can be co-located on the same chassis edge with an isolation of over 20 dB. The co-located dual-antenna prototype was fabricated and verified in the measurements.

  • 282.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lin, XianQi
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lau, B. K.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Calculating signal correlation in lossy dipole arrays using scattering parameters and efficiencies2013Ingår i: 2013 7th European Conference on Antennas and Propagation, EuCAP 2013, EurAAP , 2013, s. 519-523Konferensbidrag (Refereegranskat)
    Abstract [en]

    Correlation coefficient, as a critical performance metric of multiple antenna systems, can be calculated from the 3D radiation patterns of the antennas for multipath environments with uniform 3D angular power spectrum. A simpler, faster and lower cost approach uses the antennas' scattering parameters to determine correlation coefficient. However, the method assumes lossless antennas, and hence only achieves good accuracy for antennas with high radiation efficiencies. In this work, a method for calculating correlation coefficients in lossy dipole arrays is proposed, using only the scattering parameters and radiation efficiencies. The method is based on the equivalent circuit of antennas, and it gives a significantly better estimate of the correlation coefficient than the existing methods. The proposed method is also applied to two folded monopole antennas in a compact terminal to demonstrate its effectiveness.

  • 283.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lin, Xianqi
    Lau, Buon Kiong
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Calculation of signal correlation in lossy antenna arrays using scattering matrixArtikel i tidskrift (Övrigt vetenskapligt)
  • 284. Li, Hui
    et al.
    Lin, Xianqi
    Lau, Buon Kiong
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Equivalent Circuit Based Calculation of Signal Correlation in Lossy MIMO Antennas2013Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 61, nr 10, s. 5214-5222Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Correlation coefficient of received signals across a pair of antennas is a key performance indicator for multiple-input-multiple-output (MIMO) systems. For multipath environments with uniform 3-D angular power spectrum, the signal correlation between two antennas can be exactly calculated from their 3-D radiation patterns. When radiation patterns are unavailable, a simplified approach that only requires the antennas' scattering parameters can be used instead. However, the simpler method assumes lossless antennas and thus only works well for antennas with high radiation efficiencies. To take into account the antenna loss, the idea of equivalent circuit approximation is used in this paper to analytically separate the lossy components (resistance or conductance) from the lossy antenna arrays, using known scattering parameters and radiation efficiencies. The simplified method using S parameters can then be applied to obtain the correlation coefficient of the equivalent lossless antennas. The effectiveness of the method has been verified on antennas operating at a single mode, such as dipole or patch at its lowest resonant frequency. Good results were also obtained for the measured case of a dual-antenna mobile terminal, consisting of a monopole and a PIFA.

  • 285.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Tan, Yi
    Lau, Buon Kiong
    Ying, Zhinong
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Characteristic Mode Based Tradeoff Analysis of Antenna-Chassis Interactions for Multiple Antenna Terminals2012Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 60, nr 2, s. 490-502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The design of multiple antennas in compact mobile terminals is a significant challenge, due to both practical and fundamental design tradeoffs. In this paper, fundamental antenna design tradeoffs of multiple antenna terminals are presented in the framework of characteristic mode analysis. In particular, interactions between the antenna elements and the characteristic modes and their impact on design tradeoffs are investigated in both theory and simulations. The results reveal that the characteristic modes play an important role in determining the optimal placement of antennas for low mutual coupling. Moreover, the ability of antenna elements to localize the excitation currents on the chassis can significantly influence the final performance. To demonstrate the effectiveness of the proposed approach, a dual-band, dual-antenna terminal is designed to provide an isolation of over 10 dB for the 900 MHz band without additional matching or decoupling structures. A tradeoff analysis of bandwidth, efficiency, effective diversity gain and capacity is performed over different antenna locations. Finally, three fabricated prototypes verify the simulation results for representative cases.

  • 286.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Tan, Yi
    Lau, Buon Kiong
    Ying, Zhinong
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Isolation enhancement of compact MIMO antennas with current localizationArtikel i tidskrift (Övrigt vetenskapligt)
  • 287. Li, Hui
    et al.
    Xiong, J.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Extremely compact dual-band PIFAs for MIMO application2009Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 45, nr 17, s. 869-U20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A MIMO structure consisting of two extremely compact planar inverted-F antennas (PIFAs) (lambda/60 x lambda/20 x lambda/6) is proposed for GSM 900 MHz and 2.4 GHz wireless local area network applications. The miniaturisation of each antenna is achieved through a spiral-shaped PIFA and a capacitive load, forming a LC resonator. Both antennas have a good impedance bandwidth of 0.88-0.945 and 2.39-2.48 GHz for 0.9 and 2.4 GHz band, respectively. The two PIFA antennas are polarised orthogonally to each other, and isolation better than 228 dB is achieved in both bands without any structure etched on the ground. The predicted results are compared with the measured data and good agreement is found.

  • 288. Li, Hui
    et al.
    Xiong, J.
    Ying, Z.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Compact and low profile co-located MIMO antenna structure with polarisation diversity and high port isolation2010Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 46, nr 2, s. 108-109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A compact co-located MIMO structure with high port isolation is proposed for 2.4 GHz WLAN application. The antenna structure consists of a proximity-coupled square ring patch antenna, and a probe fed planar inverted F antenna co-located inside. The operating frequency of the two radiators is designed to be at the same frequency, and a high port isolation below -25 dB is achieved with an extremely narrow edge to edge inter-antenna space of 1 mm (0.008 lambda). The total lateral size of the co-located radiators is only 0.28 lambda x 0.28 lambda, i.e. only about 25% of the size of a half-wavelength dual-port patch antenna. The MIMO structure gives high gains (> 4.0 dB), low correlation (< 0.2), and high diversity gain (about 10 dB).

  • 289. Li, Hui
    et al.
    Xiong, Jiang
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A Compact Planar MIMO Antenna System of Four Elements With Similar Radiation Characteristics and Isolation Structure2009Ingår i: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 8, s. 1107-1110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A compact planar multiple-input-multiple-output (MIMO) antenna system of four elements with similar radiation characteristics is proposed for the whole 2.4-GHz WLAN band. It consists of two proximity-coupled fed microstrip square ring patch antennas and two lambda/4 microstrip slot antennas of the same linear polarization. These two types of antennas are printed on different sides of the substrate to reduce mutual coupling. With a novel isolation structure etched on the ground plane of the FR4 substrate, high port isolation (below -25 dB) and good MIMO performance are achieved. The overall lateral size of the MIMO system is only 0.64 lambda X 0.48 lambda, and good impedance matching (S11 < 10 dB) is achieved across the operating band for all the antenna elements. Full spherical radiation patterns are measured for the MIMO system, showing similar radiation characteristics, and the gains are above 2.3 dB across the operating band.

  • 290.
    Li, Hui
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Xiong, Jiang
    Yu, Yufeng
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A Simple Compact Reconfigurable Slot Antenna With a Very Wide Tuning Range2010Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 58, nr 11, s. 3725-3728Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple and compact slot antenna with a very wide tuning range is proposed. A 25 mm (roughly equal to lambda(H)/8, where lambda(H) corresponds to the highest frequency of the tuning range) open slot is etched at the edge of the ground. To achieve the tunability, only two lumped elements, namely, a PIN diode and a varactor diode are used in the structure. By switching the PIN diode placed at the open end of the slot, the slot antenna can resonate as a standard slot (when the switch is on) or a half slot (when the switch is off). Continuous tuning over a wide frequency range in those two modes can be achieved by adjusting the reverse bias (giving different capacitances) of the varactor diode loaded in the slot. Through optimal design, the tuning bands of the two modes are stitched together to form a very wide tuning range. The fabricated prototype has a tuning frequency range from 0.42 GHz to 1.48 GHz with S11 better than -10 dB, giving a frequency ratio (f(R) = f(u)/f(L)) of 3.52:1. The measured full spherical radiation patterns show consistent radiation characteristics of the proposed antenna within the whole tuning range.

  • 291. Li, J. S.
    et al.
    Chen, B.
    Yao, J.
    Zou, Y. Z.
    Hu, J. D.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A novel notch filter utilizing a composite right/left-handed transmission line2006Ingår i: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 48, nr 3, s. 626-628Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel notch filter based on a composite right/left-handed (CRLH) transmission line is proposed. The proposed CRLH transmission line is different-from a conventional CRLH transmission line. The novel notch filter has a large notch depth, very small loss in the passband, and very sharp transitions at the two edges of the stop-band.

  • 292. Li, J. S.
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Broadband optical modulator of fiber type2005Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 13, nr 3, s. 842-846Artikel i tidskrift (Refereegranskat)
  • 293. Li, J. S.
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Broadband traveling-wave modulator based on Si2N2O substrate2005Ingår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 254, nr 04-6, s. 236-241Artikel i tidskrift (Refereegranskat)
  • 294. Li, J. S.
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Electro-optic modulator based on Si2N2O substrate2006Ingår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 45, nr 1Artikel i tidskrift (Refereegranskat)
  • 295. Li, J.
    et al.
    Zhu, H. Y.
    He, Sailing
    Fast method for the localisation of current dipoles in the human brain2001Ingår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 39, nr 6, s. 678-680Artikel i tidskrift (Refereegranskat)
  • 296.
    Li, Jingwei
    et al.
    Zhejiang Univ, Chinese Natl Engn Res Ctr Opt Instruments, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Jiang, Wentao
    Zhejiang Univ, Chinese Natl Engn Res Ctr Opt Instruments, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Yao, Xinli
    Zhejiang Univ, Chinese Natl Engn Res Ctr Opt Instruments, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Cai, Fuhong
    Hainan Univ, Mech & Elect Engn Coll, Dept Elect Engn, Haikou 570228, Hainan, Peoples R China..
    He, Sailing
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. Zhejiang Univ, Chinese Natl Engn Res Ctr Opt Instruments, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China.
    Fast quantitative fluorescence authentication of milk powder and vanillin by a line-scan hyperspectral system2018Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 57, nr 22, s. 6276-6282Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a fast hyperspectral line-scan fluorescence imaging system to verify the feasibility of quantitative fluorescence authentication of powders. Vanillin, which is restricted for use in milk powder, especially in milk powder for infants, is mixed with milk powder in different mass concentrations (5%, 10%, 30%, 50%, 70%, and 90%). Mixed powders are located on a motorized linear stage. A 405 nm line laser is utilized to excite the fluorescence of the sample. Based on galvo scanning, we can generate a laser line with high spatial resolution and high-intensity density on the samples. An imaging spectrometer with a complementary metal-oxide semiconductor (CMOS) camera as detector is built. The spectral range of the spectrometer is 365-810 nm, with about 1 nm spectral resolution. One snapshot of the CMOS can acquire the fluorescent spatial and spectral information of a line region in 100 ms. By scanning the motorized linear stage, we obtain the fluorescence hypercube of the sample. A 100 x 1926 x 1216 hypercube, which covers an area of 15 mm x 5 mm, is obtained in 50 s. The imaging speed can be enhanced further by increasing the intensity of the excitation laser and the sensitivity of the area camera. Fully constrained least squares, a linear spectral mixture analysis, is utilized to analyze the hypercube obtained by our homemade imaging spectrometer, thus obtaining the pixel concentration of vanillin in each mixed powder. Linear regression analysis is used for the pixel concentration and mass concentration of vanillin. A linear relationship with coefficient of determination le equal to one is observed, which demonstrates the capability of fluorescence hyperspectral quantitative analysis in powders.

  • 297. Li, JiuSheng
    et al.
    Zou, YongZhuo
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    A novel power divider utilizing composite right/left-handed transmission line2006Ingår i: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 48, nr 9, s. 1776-1779Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel composite right/left-handed transmission line unit is proposed. Using the structure, a new power divider is developed. By adjusting the parameters of the capacitors and the inductors, the simulation results show that the power divider has perfectly symmetric power division at 1.24 GHz, return loss up to -38 dB with the transmitted power being close to -3 dB (-3.01 dB). In addition, the performances of the novel power divider are demonstrated experimentally.

  • 298. Li, JunLong
    et al.
    Liu, Hui
    Zhang, Shuai
    Zhang, Yuan
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Compact broadband circularly-polarised antenna with a backed cavity for UHF RFID applications2019Ingår i: IET Microwaves, Antennas & Propagation, ISSN 1751-8725, E-ISSN 1751-8733, Vol. 13, nr 6, s. 789-795Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A compact broadband circularly-polarised (CP) antenna is designed with a novel method for universal ultra-high-frequency (UHF) radio-frequency identification (RFID) readers. It is composed of a compact ring-shaped patch which aims to decrease the size of the antenna. A quadrature 3 dB coupler placed below the ground plane creates 90 degrees phase differences to generate the CP radiation of the antenna. To improve the performance of the proposed antenna and minimise its size, the authors use a coupling feeding method, an FR4 dielectric slab, and a metal cavity. The coupled feeding is implemented to eliminate the mismatching between the long probe and the ring-shaped patch, and to improve the gain over the operating band. The introduction of an FR4 dielectric slab and a cavity can reduce the antenna size and improve the impedance matching and axial-ratio (AR) bandwidth. The antenna with a backed cavity can increase the front-to-back ratio remarkably and improve the CP performance further. The measured results show that the antenna with a low profile (0.45 lambda(0) x 0.45 lambda(0) x 0.06 lambda(0) at 915 MHz) has the impedance bandwidth of 30.2% (730-990 MHz) and 3 dB AR bandwidth of 24.2% (760-970 MHz). Both the impedance and the AR bandwidth cover the worldwide UHF RFID band.

  • 299. Li, Shichao
    et al.
    Sun, Fei
    An, Di
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Increasing Efficiency of a Wireless Energy Transfer System by Spatial Translational Transformation2018Ingår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, nr 4, s. 3325-3332Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A magnetic translational projector (MTP) designed by transformation optics is applied to improve energy transfer efficiency in a wireless power transfer (WPT) system. Our numerical simulation results showtheMTP can greatly enhance energy transfer efficiency (e.g., nearly two orders, compared to the case without our MTP) in the WPT system, which is much larger than that of a previous method (i.e., using magnetic super-lens). A 3-D reduced MTPcomposed of layered isotropicmagnetic materials is designed, whose performance is verified by our 3-D numerical simulation in 10 MHz. The influence of loss in metamaterial on the performance of the proposed MTP is also studied, which shows that the MTP can still enhance energy transfer efficiency when loss exists. Further simulation is also carried out to show that the function of the MTP is not sensitive to large perturbation. Finally, detailed experimental suggestion for implementing the simplified MTP, which is composed of layered medium is given and then verified by our numerical simulation.

  • 300. Li, Wenjiang
    et al.
    Fu, Tao
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Preparation of free-standing silica 3D colloidal crystal film at water-air interface2006Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 441, nr 01-2, s. 239-244Artikel i tidskrift (Refereegranskat)
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