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  • 1401. Zhong, Shuomin
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ultrathin and lightweight microwave absorbers made of mu-near-zero metamaterials2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 2083-Article in journal (Refereed)
    Abstract [en]

    We present a theory of perfect absorption in a bilayer model composed of a mu-near-zero (MNZ) metamaterial (MM) absorbing layer on a metallic substrate. Our analytical solutions reveal that a MM layer with a large purely imaginary permeability and a moderate permittivity backed by a metallic plane has a zero reflection at normal incidence when the thickness is ultrathin. The impedance-mismatched metamaterial absorber (MA) can be 77.3% thinner than conventional impedance-matched MAs with the same material loss in order to get the same absorption. A microwave absorber using double-layered spiral MMs with a thickness of only about one percent of the operating wavelength is designed and realized. An absorption efficiency above 93% at 1.74 GHz is demonstrated experimentally at illumination angles up to 60 degrees. Our absorber is 98% lighter than traditional microwave absorbers made of natural materials working at the same frequencies.

  • 1402. Zhong, Shuomin
    et al.
    Ma, Yungui
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Centre for Optical and Electromagnetic Research, Department of Optical Engineering, Zhejiang University, China .
    Perfect absorption in ultrathin anisotropic epsilon-near-zero metamaterials2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 2, p. 023504-Article in journal (Refereed)
    Abstract [en]

    Conventionally, perfect absorption by an ultrathin material usually requires a high material loss. In this paper, this common understanding is challenged. Our analytical solution shows that an anisotropic e-near-zero thin metamaterial (MM) backed by a metallic substrate can perfectly absorb an incident plane wave at a specific angle while the MM can be arbitrarily thin and arbitrarily low-loss. The counterintuitive phenomenon is due to coherent cancelling. As a proof, we demonstrate a microwave absorber working at 5.35 GHz using low-loss meander-line MMs with a thickness of only lambda/56. An absorption peak of 95% at a 60 degrees incidence angle is obtained experimentally, which verifies the analytical results well.

  • 1403. Zhou, Bin
    et al.
    Chen, Zhuo
    Zhang, Yebin
    Gao, Shaorui
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Active Fiber Gas Sensor for Methane Detecting Based on a Laser Heated Fiber Bragg Grating2014In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 26, no 11, p. 1069-1072Article in journal (Refereed)
    Abstract [en]

    An active optical fiber gas sensor was developed in a cobalt-doped single mode fiber. This fiber can be heated up to a few hundred degrees Celsius by a heating laser, and a fiber Bragg grating (FBG) was fabricated inside this fiber as a thermometer. The Bragg wavelength of the FBG is sensitive to the thermal conductivity of the gas surrounding the fiber and can be used to monitor the concentration of a special gas once we know in advance the kind of gas. The proposed sensor is ideal for detecting explosive or corrosive gases in some practical application scenarios, such as gas pipeline, coal mine, flow meters, and so on. We have measured the methane concentration ranging from 0% to 4.8% (5% is its explosion limit) as a demonstration.

  • 1404. Zhou, Bin
    et al.
    Yan, Chunsheng
    Guan, Zuguang
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Low Coherent Optical Frequency Domain Reflectometry Interrogates Fiber Bragg Grating Sensors2010In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 28, no 21, p. 3409-3414Article in journal (Refereed)
    Abstract [en]

    A novel fiber optical reflectometry is proposed for long distance measurements and sensing applications. The reflectrometric information is included in the phase difference of two interfering light beams reflected at the same scattering point on the fiber under test (FUT). The reflection position and local information can be determined by modulating the frequency difference and analyzing the reflecting signal in frequency domain. Theoretical analysis and experimental demonstration are presented. Two adjacent reflection points 50 km away from the reflectometry with a gap of 11 meters between each other is distinguished. It is estimated that the operating range could be over 500 km theoretically by employing a light source with 0.3 nm bandwidth. This novel reflectometry is applied as a fiber Bragg grating interrogation solution as an example.

  • 1405. Zhou, Bin
    et al.
    Zhang, A. Ping
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gu, Bobo
    Cladding-Mode-Recoupling-Based Tilted Fiber Bragg Grating Sensor With a Core-Diameter-Mismatched Fiber Section2010In: IEEE PHOTONICS J, ISSN 1943-0655, Vol. 2, no 2, p. 152-157Article in journal (Refereed)
    Abstract [en]

    We demonstrate a reflective fiber-optic sensor with a core-diameter-mismatched fiber section and cladding-mode recoupling in a tilted fiber Bragg grating (TFBG). High-order cladding modes are efficiently excited by either a multimode fiber or a thin-core fiber section and recoupled back to the core mode by the TFBG. A special reflection spectrum with recoupling of cladding mode is then obtained to exploit the applications of evanescent waves in an optical fiber. Experimental results of the sensor to measure the external refractive index are presented.

  • 1406. Zhou, F.
    et al.
    Liu, Q.
    Zhao, Kun
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A dual-band loop MIMO antenna for smart watch applications2016In: 2016 Progress In Electromagnetics Research Symposium, PIERS 2016 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 1262-1266Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a dualband loop MIMO antenna with Wi-Fi 2.4/5.2/5.8 GHz bands for smart watch applications. The antenna is constituted of a 25-mm long folded loop strip and an L-shape coupling strip. Two antenna elements are put at the adjacent side of the ground and are vertical to the system ground. With the coupling strip, the loop antenna can generate a quarter-wavelength resonant mode at about 2.45 GHz and a higher order mode cover 5.2 GHz and 5.8 GHz. The dimension of the system ground is 38mm × 38mm × 0.3mm and a 2mm gap between the antenna and the ground is set to alleviate the strong coupling between the antenna and the ground. The simulation results show the MIMO antenna system have good S11 and S12 performance across 2.4 GHz to 2.5 GHz and 5.2 GHz to 5.8 GHz. Further, as the antenna system is dedicated to be embedded in a smart watch, the body effect and the SAR are also investigated in the research.

  • 1407. Zhou, H
    et al.
    Diendorfer, G.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, H.
    Mair, M.
    The influence of meteorological conditions on upward lightning initiation at the Gaisberg Tower2014In: 2014 International Conference on Lightning Protection, ICLP 2014, 2014, p. 1162-1165Conference paper (Refereed)
    Abstract [en]

    Meteorological parameters associated with the initiation of upward lightning discharges from a tall tower were investigated. The parameters, including temperature, wind speed, air pressure, and relative humidity, were measured at the Gaisberg Tower top and at a distance of 170 m from the tower. A comparison of parameters associated with self-initiated upward flashes (initiated without any nearby preceding lightning activity) and nearby-lightning-triggered upward flashes (triggered by nearby preceding lightning activity) was made. It shows that at the Gaisberg Tower (GBT), relatively low ambient temperature facilitates to initiate upward flashes without any nearby preceding lightning activity. Relatively high ambient temperature (8.5 °C to 15.5 °C) facilitates to initiate upward positive stepped leaders, rather than the common continuous leaders, in the self-initiated upward negative flashes. No reliable correlation between wind speed and upward initiation of lightning was found.

  • 1408. Zhou, H.
    et al.
    Ding, F.
    Jin, Y.
    He, Sailing L.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    TERAHERTZ METAMATERIAL MODULATORS BASED ON ABSORPTION2011In: PROG ELECTROMAGN RES, ISSN 1559-8985, Vol. 119, p. 449-460Article in journal (Refereed)
    Abstract [en]

    Metamaterial absorbers can perfectly absorb an incident wave in a narrow frequency band. In this paper, metamaterial absorbers are used to construct a terahertz modulator. By controlling the carrier density in the n-doped semiconductor spacer between a patterned metallic superstructure and a metallic ground with different applied voltage bias, the absorption varies sensitively, and the reflected wave amplitude acting as the modulated signal can be strongly modulated. Two types of modulators are investigated, one of which possesses an array of metallic crosses as the superstructure, and the other has a complementary superstructure. Compared with the former, the latter may give a better modulation performance.

  • 1409.
    Zhou, Helin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Experimental Observations and Theoretical Modeling of Lightning Interaction with Tall Objects2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates various discharge processes associated with upward lightning initiated from tall objects, both experimentally and theoretically, trying to bridge the knowledge-gap in understanding the mechanisms of the phenomena.

    Upward lightning initiation has attracted a great deal of interest during recent years due to the proliferation of tall communication towers and wind turbines.  Simultaneous lightning current waveforms, close electric field changes, and lightning location system data associated with upward lightning measured at the instrumented Gaisberg Tower (GBT) near Salzburg in Austria from 2005 to 2009 is studied. It was observed  that a majority of upward flashes (87%) were self-initiated, namely they were initiated at the tower top without any nearby preceding discharge activity, whereas only  26 (13%) upward flashes were nearby-lightning-triggered, namely they were triggered by nearby preceding lightning discharges occurring within 100 milliseconds or so. This observation is different from the study conducted in Rapid City in South Dakota of USA where they observed the majority of upward flashes (80/81) initiated from ten tall towers were nearby-lightning-triggered. The possible reasons for self-initiated upward flashes dominating at the GBT could be (1) the field enhancement due to the shape of Gaisberg Mountain which is more than 800 m above the surrounding terrain of the city of Salzburg and (2) low altitude of charge region in the cloud during non-convective season (September to March) in Austria.

    Three modes of charge transfer had previously been identified in cloud-to-ground lightning, namely that happens during leader-return stroke sequence, during continuing current and during M-components. On the basis of the analysis of the simultaneous current, electric field changes, and high-speed video images measurements, a mixed mode of charge transfer to ground for ICC pulses and M-components in tower-initiated (upward) lightning is proposed. Compared to classical rocket-triggered lightning, occurrence of multiple branches of upward lightning from tall towers is very common. A newly illuminated or re-illuminated branch connecting to the already luminous channel attached to the tower during initial continuous current and continuing current following return strokes is frequently observed. A mixed mode of charge transfer to ground is composed of a new or decayed branch involving the leader/return-stroke mode of charge transfer to ground, and superimposing on the old channel with continuous (continuing) current mode of charge transfer to ground. This mode can explain ICC pulses exhibiting shorter risetimes, larger peaks, and shorter half-peak widths than “classical” M-components as reported in previous studies.

    Charge density expressions for the tall object and lightning channel when lightning strikes a tall object are derived based on continuity equation and current expressions given by the series point current source model representation of the tall object and lightning channel. Validation of charge density expressions was performed by comparing the total vertical electric field at ground level calculated by the traditional dipole technique with that calculated by the monopole technique using charge density expressions derived above. Distribution of charge density versus height along the tall object and along the lightning channel by considering the different values of current reflection coefficient at strike object base and the return stroke front speed in the lightning channel has provided an alternative way to explain the polarity inversion of vertical electrical field at very close range from strike object base.

    Characteristics of upward positive and bipolar lightning flashes observed from the GBT during 2000-2009 are studied in detail. A total of 26 upward positive flashes and 21 upward bipolar flashes were identified, which only accounted for 4% and 3%, respectively, of the total 652 flashes measured at the GBT during the 10-year observation period. There are only very few previous studies of upward positive and bipolar flashes. Bipolar flashes lower both negative and positive charges during different phases with the same flash. In the positive flashes, median values for flash peak current, flash duration, flash charge transfer, and flash action integral were determined as 5.2 kA, 82 ms, 58 C and 0.16×103 A2s, respectively. From simultaneous current and high-speed video measurements of one bipolar flash it is inferred that sub-branches are connected to one branch transferring both positive and negative charges successively, running into charge source regions of opposite polarity in the thundercloud. 

  • 1410.
    Zhou, Helin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Some Properties of Lightning Flashes to a Tall Tower on a Mountain Top2012Licentiate thesis, comprehensive summary (Other academic)
  • 1411.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, G.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, H.
    Fair-weather atmospheric electric field measurements at the Gaisberg Mountain in Austria2011In: Prog. Electromagn. Res. Symp., 2011, p. 1303-1307Conference paper (Refereed)
    Abstract [en]

    A field mill (FM) has been permanently operated at a distance of about 170m from the Gaisberg Tower (GBT) in Austria since several years. The electric field measurements suffer from field enhancement due to its location on a 4-m tall metal platform near the tower which itself is located on a 1280 meter high mountain. A special measuring campaign was conducted to determine the fair-weather atmospheric electric field at the Gaisberg Mountain on June 24th, 2010. The main objectives of this campaign were to calibrate the field mill in order to infer the relation between the electric fields at the tower tip and the ground level measured by the field mill under thunderstorm conditions. Besides the permanent field mill near the tower, two Campbell Scientific CS100 electric field meters were used during this campaign, and distances between each other were determined by using the Global Positioning System (GPS). Overall we determined an enhancement factor of 2.75 due to the mountain itself with reference to the mountains surrounding terrain. A field enhancement factor of 7.81 was obtained for the permanently installed field mill at the measurement platform next to the GBT with reference to the undisturbed electric field at the mountain top close to the platform at ground level. The electric field near the tower (distances about the tower height of 100 m) was smaller than the field measured at larger distance from the Tower. This observation was possibly caused by a shadowing effect of the tower.

  • 1412.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, G.
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, H.
    Austrian Electrotechnical Association, Vienna, Austria..
    Mair, M.
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Close electric field changes associated with upward-initiated lightning at the Gaisberg Tower2011In: 2011 International Symposium on Lightning Protection, XI SIPDA 2011, 2011, p. 87-90Conference paper (Other academic)
    Abstract [en]

    We examine in detail the simultaneous lightning current waveforms, close electric field changes, and lighting location system data for upward lightning discharges initiated from the Gaisberg Tower (GBT) from 2005 to 2009. Out of 205 upward flashes, we find that most of upward flashes (179/205 or 87%) are initiated at the tower top without any nearby preceding discharge activity, 26 flashes (13%) are initiated by nearby triggering lightning discharges, including 10 positive cloud-to-ground lightning, 1 negative cloud-to-ground lightning, and 15 cloud discharges. The possible reasons for self-triggered upward flashes dominating at the GBT would be the field enhancement due to the Gaisberg Mountain above 800 m of the surrounding terrain of the city of Salzburg and low cloud base during cold season.

  • 1413.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, G.
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, H.
    Austrian Electrotechnical Association, Vienna, Austria..
    Mair, M.
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Mixed mode of charge transfer to ground for initial continuous current pulses in upward lightning2011In: 2011 7th Asia-Pacific International Conference on Lightning (APL), 2011, p. 677-681Conference paper (Refereed)
    Abstract [en]

    In this paper, we discuss properties of initial continuous current (ICC) pulses superimposed on the slow varying initial stage current in upward flashes initiated from the Gaisberg Tower (GBT) based on simultaneous current, near/far electric field measurements. ICC pulses are usually associated with M-component mode of charge transfer to ground, if only one branch of the lightning channel is active. However, there are several cases in which ICC pulses involve a predominantly leader/return-stroke mode of charge transfer to ground in a new channel that connects to the old channel carrying continuous current. With the help of high-speed video camera records, we find that this mixed mode of charge transfer for ICC pulses, leader-return stroke in one channel and continuous current in another channel, occurring simultaneously during the initial stage current in upward lightning from tall towers is very common. This is in contrast to triggered-lightning where usually only one channel is dominant and ICC pulses are associated predominantly with M-component mode of charge transfer. Also, ICC pulses with mixed-mode of charge transfer have shorter risetimes, larger peaks, and shorter half-peak widths.

  • 1414.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Mair, Martin
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    A Preliminary Analysis of Bipolar Lightning Observed to the Gaisberg Tower from 2000 to 20072009Conference paper (Other academic)
  • 1415.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association, Dept. ALDIS, Vienna, Austria.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Austrian Electrotechnical Association, Dept. ALDIS, Vienna, Austria.
    Mair, Martin
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Characteristics of upward bipolar lightning flashes observed at the Gaisberg Tower2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. D13106-Article in journal (Refereed)
    Abstract [en]

    We analyze current records for 21 upward initiated bipolar lightning flashes observed at the Gaisberg Tower (GBT) in Austria from 2000 to 2009. A bipolar lightning flash occurrence of 3% (21/652) is found during the 10-year observation period. Thirteen (62% or 13/21) of them occurred in nonconvective season (September-March). On the basis of the classification suggested by Rakov and Uman (2003), 13 (62%) of the 21 bipolar flashes belong to Type 1 associated with a polarity reversal during the initial stage (IS) current, five belong to Type 2 associated with different polarities of the IS current and the following return strokes, one belongs to Type 3 associated with return strokes of opposite polarity following the IS, and two of them are not assigned. We also find that the initial polarity reversal from negative to positive occurs more often (76% or 16/21) than that from positive to negative within a bipolar flash, in agreement with observations in other studies. The geometric mean (GM) and arithmetic mean (AM) of the total absolute charge transfer are 99.5 C and 125 C, with the GM and AM total flash duration of 320 ms and 396 ms, respectively. From simultaneous current and high-speed video measurements of one bipolar flash, within the field of view, the positive charge was transferred along one branch initially, followed by the negative charge transfer after cessation of the luminosity for 142 ms, while the other two branches connected to the main channel always contributed to the negative charge transfer during the whole process.

  • 1416.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association, Dept. ALDIS, Vienna, Austria.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Austrian Electrotechnical Association, Dept. ALDIS, Vienna, Austria.
    Mair, Martin
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Characteristics of upward positive lightning flashes initiated from the Gaisberg Tower2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, no 6, p. D06110-Article in journal (Refereed)
    Abstract [en]

    We report the measured current characteristics of positive lightning discharges to the Gaisberg Tower (GBT) in Austria from 2000 to 2009. On the basis of the recorded current waveforms, a total of 26 flashes consisting of initial stage only were identified as upward positive discharges initiated by an upward negative leader from GBT. They accounted for 4% (26/652) of the total flashes recorded at the GBT. Nineteen (73%) out of the 26 positive flashes occurred during nonconvective season (September-March). Median values of flash peak current, flash duration, charge transfer, and action integral were determined as 5.2 kA, 82 ms, 58 C, and 0.16 x 10(3) A(2) s, respectively. Current pulses of high repetition rate superimposed on the initial portion of initial continuous current are inferred to be associated with the upward negative stepped leader process. The weighted arithmetic means of leader pulse peak current, leader pulse duration, leader interpulse interval, and leader pulse charge are 3 kA, 31 mu s, 32 mu s, and 42 mC, respectively. On the basis of an assumed stepped leader speed in the range of 8 x 10(4) to 4.5 x 10(5) m/s an upward negative stepped leader channel charge density of 15-87 mC/m, a leader length of 168-945 m, and an average leader step length of 2.4-13.3 m were estimated. The upward negative stepped leader channel charge density and length are significantly larger and smaller than their counterparts in downward negative stepped leaders, respectively, while the upward leader step length is consistent with previous studies. Possible reasons for this are discussed.

  • 1417.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Mair, Martin
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Continuing Current in Tower-Initiated Lightning2010In: 2010 30th International Conference on Lightning Protection, ICLP 2010, Institute of Electrical and Electronics Engineers (IEEE), 2010, article id 7845865Conference paper (Refereed)
    Abstract [en]

    We investigate 172 upward-initiated negative lightning flashes containing at least one leader-return stroke sequence observed to the Gaisberg Tower (GBT) in Austria from 2000 to 2009. A geometric mean value of 8.75 kA of the return stroke peak current is determined, followed by a continuing current of 1.48 ms with a charge transfer of 0.786 C. We find that in case of the continuing current duration larger than 40 ms, usually defined as long continuing current, or when the continuing current charge transfer is greater than 5 C, the initiating peak return stroke current did not exceed 20 kA. Moreover, continuing currents with durations of less than 20 ms or with a charge transfer smaller than 5 C, those continuing currents were initiated by return strokes with peaks of any range.

  • 1418.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association, Dept. ALDIS, Vienna, Austria.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Austrian Electrotechnical Association, Dept. ALDIS, Vienna, Austria.
    Mair, Martin
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Measured current and close electric field changes associated with the initiation of upward lightning from a tall tower2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. D08102-Article in journal (Refereed)
    Abstract [en]

    We examine in detail the simultaneous lightning current waveforms, close electric field changes, and lightning location system data for upward lightning discharges initiated from the Gaisberg Tower (GBT) from 2005 to 2009. Out of 205 upward flashes, most of them (87% or 179/205) were initiated from the tower top without any nearby preceding lightning activity (called "self-initiated"), whereas 26 upward flashes (13%) were initiated from the tower top with immediately preceding nearby lightning activity (called "nearby-lightning-triggered"), including 15 positive ground flashes, one negative ground flashes, and 10 cloud discharges. The possible reasons for self-initiated upward flashes dominating at the GBT could be the field enhancement due to the Gaisberg Mountain above the surrounding terrain and low altitude of charge region during non-convective season (September to March), since we note that self-initiated lightning at the GBT occurred predominantly (79% or 142/179) during non-convective season. On the other hand the majority (85% or 22/26) of nearby-lightning-triggered upward flashes at the GBT occurring during convective season (April to August) and 80 nearby-lightning-triggered upward flashes out of 81 upward flashes observed at the ten tall towers in Rapid City in South Dakota of USA occurring during summer seasons, could be due to the result of high altitude of charge region. The triggering flashes were detected to be within 1 and 18 km distance and the time intervals between them and upward lightning initiation are in the range of 0.3 to 90.7 ms.

  • 1419.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Mair, Martin
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Simultaneous current and electric field observations of upward negative leaders initiated from the Gaisberg Tower2010In: 2010 Asia-Pacific Symposium on Electromagnetic Compatibility, APEMC 2010, 2010, p. 1174-1177Conference paper (Other academic)
    Abstract [en]

    In this paper, we present simultaneous current and electric field records of two upward negative leaders initiated from the Gaisberg Tower (GBT). It is shown that bipolar current pulses occur at the beginning of the upward negative leaders followed by regular unipolar leader pulse trains, and the corresponding electric field exhibits asymmetrical V-shaped pulses with a hump superimposed at the end of the pulse. The stepped leader characteristics in electric field waveforms at close range are similar to that of downward stepped leader pulses in altitude-triggered lightning flashes. Distinct electric field changes prior to the upward negative leader inception are indicative of nearby lightning discharges.

  • 1420.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Mair, Martin
    Central Institute for Meteorology and Geodynamics, Vienna, Austria.
    Upward Bipolar Lightning Flashes Observed at the Gaisberg Tower2010Conference paper (Other academic)
  • 1421.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rakov, Vladimir A.
    Diendorfer, Gerhard
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, Hannes
    Mair, Martin
    A study of different modes of charge transfer to ground in upward lightning2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 125, p. 38-49Article in journal (Refereed)
    Abstract [en]

    We examined simultaneous measurements of currents and close electric field changes, as well as highspeed video images, associated with pulses superimposed on the initial continuous current (ICC pulses) and M-components following return strokes in upward flashes initiated from the Gaisberg Tower in Austria. For tower-initiated lightning, upward leaders often create multiple branches below the cloud base that can facilitate initiation of transients at relatively low heights along the grounded channel carrying ICC of some tens to hundreds of amperes. In this situation, a conducting channel is present, which is necessary for the M-component mode of charge transfer to ground, but the excitation wave (leader), after entering the channel, cannot form a long-front downward M-wave, because of the relatively short distance between the entry (junction) point and the strike-object top. Clearly, two parallel channels, one previously existing and the other newly formed (or rejuvenated) are involved in the charge transfer, and there is a common channel section between the junction point and the strike object. We use the term "mixed mode of charge transfer to ground", to indicate that in the case of low junction point the "classical" M-component mode is not possible, even though a conducting channel to ground (an attribute of the M-component mode) is present. The mixed mode scenario is also applicable to impulsive processes during continuing currents following return strokes in upward lightning.

  • 1422.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Theethayi, Nelson
    Bombardier Transportation, Sweden.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association (ÖVE), Vienna.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rakov, Vladimir
    University of Florida, Gainesville, USA.
    A New Approach To Estimation Of Effective Height Of Towers On Mountain Tops For Lightning Incidence Studies: Sensitivity Analysis2009Conference paper (Other academic)
    Abstract [en]

    In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop based on the statistical observations . We derive the effective heights based on Rizk’s lightning attachement model, which are less than those predicted by the earlier methods based on statistical observations. Then we perform sensitivity analysis to evaluate the effect of uncertainties in model parameters that influence the effective height. Variations in the effective height as a function of model parameters, including the final quasi-stationary leader gradient, minimum positive streamer gradient, upward connecting positive leader speed, and mountain base radius, are presented, with Gaisberg tower as the example. It’s found that the effective height depends primarily on the structre height, mountain shape and upward positive leader speed. This new approach presented here can be employed to estimate the effective height for towers for which no lightning incidence data needed for the earlier methods are available. And the information could be also used in designing lightning protection of communication/transmission line towers and masts on mountain tops.

  • 1423.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Theethayi, Nelson
    Bombardier Transportation Sweden, Västerås, Sweden.
    Diendorfer, Gerhard
    Austrian Electrotechnical Association, Dept. ALDIS, Vienna, Austria.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rakov, Vladimir A.
    Department of Electrical and Computer Engineering, University of Florida, Gainesville, USA.
    On estimation of the effective height of towers on mountaintops in lightning incidence studies2010In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 68, no 5, p. 415-418Article in journal (Refereed)
    Abstract [en]

    Towers on mountaintops have more incidence of lightning than towers on the flat ground. Therefore towers on mountaintops are ascribed an effective height that is often considerably larger than the physical height of the tower. In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop and propose a new definition based on an engineering model of lightning attachment. The results can be useful in designing lightning protection of communication/transmission lines and masts on mountaintops.

  • 1424.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, G.
    Calculation of electromagnetic fields in free space when lightning strikes a tall object2013In: 2013 International Symposium on Lightning Protection (XII SIPDA), IEEE Computer Society, 2013, p. 91-95Conference paper (Refereed)
    Abstract [en]

    We calculate vertical electric field and azimuthal magnetic field at different elevation angles and distances associated with lightning strikes a tall object. Simple and exact expressions for electromagnetic fields are derived when the current reflection coefficient at tall object top is zero and return stroke propagation speed in the lightning channel is equal to the speed of light. Further, we investigate the effects of current reflection coefficient at tall object top being not zero and the propagation speed is less than the speed of light (e.g., one half) on electromagnetic fields. Interestingly, we find that the vertical electric field has its largest peak value either at the smallest elevation angle or at the largest elevation angle. While for the azimuthal magnetic field, we note that its largest peak value is always at the smallest elevation angle or relatively small elevation angles.

  • 1425.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    A new approach to calculate electric fields and charge density distribution when lightning strikes a tall object2014In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 113, no SI, p. 15-24Article in journal (Refereed)
    Abstract [en]

    We derive electric field expressions, associated with lightning strikes to a tall object, using the monopole (Continuity Equation) technique which is distinctly different from the traditional dipole (Lorentz Condition) technique. Expressions to calculate the charge density along the tall object and lightning channel based on the assumptions of the transmission line model of the lightning strikes to a tall object and a series point current source placed at the object top, are also derived. These expressions are used to calculate the very close-range electric fields in the monopole (Continuity Equation) technique in terms of the retarded current and charge density along the tower and lightning channel and their results are compared with those calculated from the traditional dipole (Lorentz Condition) technique in terms of the retarded current along the tower and lightning channel. Alternative explanations are provided to the inversion of polarity of the vertical electric field at very close range based on distribution of charge density along the tower and lightning channel.

  • 1426.
    Zhou, Helin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Diendorfer, Gerhard
    Distribution of charge along the tower and lightning channel when lightning strikes a tall tower2012In: 2012 31st International Conference on Lightning Protection, ICLP 2012, IEEE , 2012, p. 6344342-Conference paper (Refereed)
    Abstract [en]

    We derive expressions to calculate the charge density along the tower and lightning channel based on the assumptions of the transmission line model of the lightning strikes to a tall tower and a series point current source placed at the tower top. These expressions are used to calculate the very close-range electric fields in the monopole (continuity equation) technique in terms of the retarded current and charge density along the tower and lightning channel and their results are compared with those calculated from the traditional dipole (Lorentz condition) technique in terms of the retarded current along the tower and lightning channel. Alternative explanations are provided to the inversion of polarity of the vertical electric field at very close range based on distribution of charge density along the tower and lightning channel.

  • 1427. Zhu, B.
    et al.
    Lv, F.
    Ma, D.
    Zhou, Helin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A pocket discharge model for narrow bipolar events and possible applications2010In: 2010 Asia-Pacific Symposium on Electromagnetic Compatibility, APEMC 2010, 2010, p. 1558-1561Conference paper (Refereed)
    Abstract [en]

    Narrow bipolar events refer to a distinct type of in-cloud lightning discharge which produces electric field of bipolar and impulse in nature. In this presentation narrow bipolar events were considered as the discharge of the pocket charge to the charge layer inside thundercloud, and the current wave-shape possibly responsible for the narrow bipolar electromagnetic field was featured by two channel-conducting-state depended parameters (α,β). The parameter β inversely reflects the time for the current front to propagate along the channel and can be achieved by the perfect fit of the measured field waveform to the model field waveform with the channel length and current propagation speed bound by the parameter β. The present model was applied to the narrow bipolar fields of two narrow bipolar events to reach a parameter β of 0.333μs-1 and 0.353μs-1 respectively, indicating a channel length less than 1km.

  • 1428. Zhu, Baoyou
    et al.
    Zhou, Helin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rakov, Vladimir A.
    Simultaneous observations of electric field changes, wideband magnetic field pulses, and VHF emissions associated with K processes in lightning discharges2014In: Journal of Geophysical Research D: Atmospheres, ISSN 2169-897X, Vol. 119, no 6, p. 2699-2710Article in journal (Refereed)
    Abstract [en]

    We studied simultaneous electric field changes, microsecond-scale (VLF/LF) magnetic field pulses, and VHF emissions associated with K processes in 37 cloud and 54 cloud-to-ground lightning flashes that occurred in a local convective thunderstorm in Shanghai. All the observed features were very similar for both types of flashes. Over 98% of the 1252 observed K changes were associated with detectable microsecond-scale pulses, although only about 26% of them were accompanied by large pulses whose amplitude exceeds by at least 50% the average amplitude of the five largest pulses in the flash. VHF bursts, which almost always coincide in time with microsecond-scale pulses, can occur either during K changes or during the gaps between K changes. About 9% of K changes were observed to be associated with regular pulse trains, with pulses in the train showing one-to-one correspondence to VHF bursts and occurring at a geometric mean interval of 6.9 mu s. Overall, our results indicate that small microsecond-scale pulses are an inherent feature of K processes. We infer that the K process can be viewed as a fast negative leader, but only those leaders with appreciable charge transfer show step/ramp-like K changes in electric field records.

  • 1429. Zhu, H.
    et al.
    Cai, T.
    Xu, J.
    Wu, S.
    Li, X.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. South China Normal University (SCNU), China.
    Neural correlates of stereoscopic depth perception: A fNIRS study2016In: 2016 Progress In Electromagnetics Research Symposium, PIERS 2016 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 4442-4446, article id 7735646Conference paper (Refereed)
    Abstract [en]

    The aim of the present study was to explore the brain region correlated with stereoscopic depth perception with different degree of binocular disparities. fNIRS was used to measure the neural activity of the occipital cortex induced by random-dot stereogram (RDS) with disparities from 0.1° to 1.5° and analyzed the strength and activation pattern from participants with left and right eyedness. Results revealed that the visual cortex was spatial correlated with the binocular disparity and there was a left lateralization effect for right-eye-dominant participants. Furthermore, binocular disparity around 0.5° led the strongest activation, whereas binocular disparity exceed 1.1° led lower activation which could be caused by visual fatigue. The present study supported the feasibility of fNIRS to assess the neural correlates of stereoscopic depth perception, to optimize the stereoscopic vision, and to objective evaluation of visual fatigue.

  • 1430. Zhu, H.
    et al.
    Fan, Y.
    Li, X.
    Huang, D.
    Guo, H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Some effects of specific interest on the brain of children with autism spectrum disorder (ASD): A functional near-infrared spectroscopy study2015Conference paper (Refereed)
    Abstract [en]

    Autism spectrum disorder (ASD) is a neuro-developmental disorder, characterized by two major domains: impairments in the social cognition and communication as well as restricted, repetitive, stereotyped interests and behaviors. In this study, functional near-infrared spectroscopy (fNIRS) was applied to investigate the atypical activation pattern of language areas (bilateral inferior frontal gyrus and bilateral temporal cortex) and uncover the impact of a specific interest on the brain function of children with ASD. We employed a listening comprehension task to stimulate the language areas of 2 ASD boys (A1 and A2) who had strong interests in the experiment material ("Lightning McQueen") and another 2 ASD boys (A3 and A4) who were matched with A1 and A2 respectively by age, intelligence quotient, language ability and the severity of symptoms. Our results showed that, during the task, the picture of "Lightning McQueen", but not the words of "The little red car", elicited stronger activation in the bilateral inferior frontal gyrus and temporal cortex of A1 and A2 than A3 and A4. These results could facilitate our understanding of language development of ASD and reconsider the role of specific interests (especially visual stimuli) played in the brain functional development of ASD.

  • 1431. Zhu, Huilin
    et al.
    Fan, Yuebo
    Guo, Huan
    Huang, Dan
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Reduced interhemispheric functional connectivity of children with autism spectrum disorder: evidence from functional near infrared spectroscopy studies2014In: Biomedical Optics Express, ISSN 2156-7085, E-ISSN 2156-7085, Vol. 5, no 4, p. 1262-1274Article in journal (Refereed)
    Abstract [en]

    Autism spectrum disorder (ASD) is a neuro-developmental disorder, which has been associated with atypical neural synchronization. In this study, functional near infrared spectroscopy (fNIRS) was used to study the differences in functional connectivity in bilateral inferior frontal cortices (IFC) and bilateral temporal cortices (TC) between ASD and typically developing (TD) children between 8 and 11 years of age. As the first report of fNIRS study on the resting state functional connectivity (RSFC) in children with ASD, ten children with ASD and ten TD children were recruited in this study for 8 minute resting state measurement. Compared to TD children, children with ASD showed reduced interhemispheric connectivity in TC. Children with ASD also showed significantly lower local connectivity in bilateral temporal cortices. In contrast to TD children, children with ASD did not show typical patterns of symmetry in functional connectivity in temporal cortex. These results support the feasibility of using the fNIRS method to assess atypical functional connectivity of cortical responses of ASD and its potential application in diagnosis.

  • 1432. Zhu, Huilin
    et al.
    Li, Jun
    Fan, Yuebo
    Li, Xinge
    Huang, Dan
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Atypical prefrontal cortical responses to joint/non-joint attention in children with autism spectrum disorder (ASD): A functional near-infrared spectroscopy study2015In: Biomedical Optics Express, ISSN 2156-7085, E-ISSN 2156-7085, Vol. 6, no 3, p. 690-701Article in journal (Refereed)
    Abstract [en]

    Autism spectrum disorder (ASD) is a neuro-developmental disorder, characterized by impairments in one's capacity for joint attention. In this study, functional near-infrared spectroscopy (fNIRS) was applied to study the differences in activation and functional connectivity in the prefrontal cortex between children with autism spectrum disorder (ASD) and typically developing (TD) children. 21 ASD and 20 TD children were recruited to perform joint and non-joint attention tasks. Compared with TD children, children with ASD showed reduced activation and atypical functional connectivity pattern in the prefrontal cortex during joint attention. The atypical development of left prefrontal cortex might play an important role in social cognition defects of children with ASD.

  • 1433. Zhu, Jianfei
    et al.
    Jiang, Wei
    Liu, Yichao
    Yin, Ge
    Yuan, Jun
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China; South China Normal University, China.
    Ma, Yungui
    Three-dimensional magnetic cloak working from d.c. to 250 kHz2015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, article id 8931Article in journal (Refereed)
    Abstract [en]

    Invisible cloaking is one of the major outcomes of the metamaterial research, but the practical potential, in particular for high frequencies (for example, microwave to visible light), is fatally challenged by the complex material properties they usually demand. On the other hand, it will be advantageous and also technologically instrumental to design cloaking devices for applications at low frequencies where electromagnetic components are favourably uncoupled. In this work, we vastly develop the bilayer approach to create a three-dimensional magnetic cloak able to work in both static and dynamic fields. Under the quasi-static approximation, we demonstrate a perfect magnetic cloaking device with a large frequency band from 0 to 250 kHz. The practical potential of our device is experimentally verified by using a commercial metal detector, which may lead us to having a real cloaking application where the dynamic magnetic field can be manipulated in desired ways.

  • 1434. Zhu, Jing-Jing
    et al.
    Zhang, A. Ping
    Xia, Tian-Hao
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Xue, Wei
    Fiber-Optic High-Temperature Sensor Based on Thin-Core Fiber Modal Interferometer2010In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 10, no 9, p. 1415-1418Article in journal (Refereed)
    Abstract [en]

    We present a new fiber-optic high-temperature sensor based on a thin-core fiber (TCF) modal interferometer. A thin-core fiber, whose core radius is about half of the radius of a standard single-mode fiber (SMF), is inserted between standard SMFs to form an extremely simple in-fiber modal interferometer. The wavelength of the transmission dip increases linearly with the temperature. Experimental demonstration shows that it can be used to sense temperature up to 850 degrees C with a sensitivity of about 18.3 pm/degrees C.

  • 1435. Zhu, K.
    et al.
    Ou, H.
    Hu, Y.
    Fu, H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    All-optical frequency up-conversion and demultiplexing with a fiber-ring-based microwave photonic filter in an IM-DD radio-over-fiber system2008In: Optical Transmission, Switching, and Subsystems VI, 2008, Vol. 7136Conference paper (Refereed)
    Abstract [en]

    In this paper, the authors present and experimentally demonstrate an all-optical frequency up-conversion and demultiplexing method in a radio-over-fiber (RoF) system. A Mach-Zehnder modulator (MZM) and a microwave photonic filter based on a fiber ring structure are used to simultaneously realize the frequency up-conversion and demultiplexing functions. In this proposed system, only a fiber ring and a photodiode (PD) are needed in the base station (BS) to fulfill the signal processing functions. This simple solution makes the base stations more cost-effective, and shows good application potential in the future radio-over-fiber systems.

  • 1436. Zhu, Kun
    et al.
    Ou, Haiyan
    Fu, Hongyan
    Remb, Edvin
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Simple and Tunable Single-Bandpass Microwave Photonic Filter of Adjustable Shape2008In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 20, no 21-24, p. 1917-1919Article in journal (Refereed)
    Abstract [en]

    A simple and tunable single-hand pass microwave photonic filter of adjustable shape is proposed and experimentally demonstrated. The filter is based on multiple sources (spectrum-sliced by a Mach-Zehnder interferometer) and two cascaded incoherent optical structures, namely, a dispersion medium of 50-km single-mode fiber and a fiber ring delay line. In the experimental range from 1.0 to 3.8 GHz, a discretely tunable single-hand pass filter with a high Q-factor or a flat-top response is achieved by carefully matching the transfer functions of the two individual optical structures.

  • 1437. Zhu, Kun
    et al.
    Ou, Haiyan
    Ye, Chenhui
    Fu, Hongyan
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    All-optical coherence-free microwave filter with switchable passbands based on phase and intensity hybrid modulation2011In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 284, no 1, p. 140-143Article in journal (Refereed)
    Abstract [en]

    A simple all-optical coherence-free microwave notch filter is proposed and experimentally demonstrated. The filter with switchable passbands is based on a single-wavelength optical source and phase-intensity hybrid modulation scheme. The DC bias voltage applied to the Mach-Zehnder intensity modulator can be adjusted to switch signs of the tap coefficients, which affect the baseband response. Both lowpass and bandpass filtering responses are observed in the experiment and agree well with the simulated results.

  • 1438.
    Zhu, Ning
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Song, Jun
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Cross-Order Echelle Grating Triplexer Based on Amorphous Silicon Nanowire Platform2008In: 2008 7TH INTERNATIONAL CONFERENCE ON THE OPTICAL INTERNET (COIN), NEW YORK: IEEE , 2008, p. 37-38Conference paper (Refereed)
    Abstract [en]

    We present fabrication and measurement results of an ultracompact silicon-on-insulator-based echelle-grating triplexer, which uses different diffraction orders to cover a large spectral range from 1.3 mu m to 1.5 mu m, with a footprint of 150 mu m x 200 mu m.

  • 1439.
    Zhu, Ning
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Song, Jun
    KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Experimental demonstration of a cross-order echelle grating triplexer based on an amorphous silicon nanowire platform2009In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 3, p. 383-385Article in journal (Refereed)
    Abstract [en]

    We present the design, fabrication, and characterization of an ultracompact silicon-on-insulator-based echelle grating triplexer. It is based on the cross-order design, which utilizes different diffraction orders to cover a large spectral range from 1.3 to 1.5 mu m with three channels located at 1310, 1490, and 1550 nm and with a footprint of 150 mu m X 130 mu m.

  • 1440. Zou, Y.
    et al.
    Hu, X.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, China.
    Lin, Z.
    Compact coplanar waveguide low-pass filter using a novel electromagnetic bandgap structure2006In: 7th International Symposium on Antennas, Propagation and EM Theory, Proceedings, 2006, p. 1039-1042Conference paper (Refereed)
    Abstract [en]

    In the present paper, a new electromagnetic bandgap (EBG) structure is proposed to design and fabricate low-pass filters on coplanar waveguide (CPW). Using the novel EBG structure, the filter prototypes exhibit sharp cutoff and low insertion loss in the passband. An equivalent lumped L-C circuit mode is introduced to describe the proposed EBG structure, which manifests an elliptic-function low-pass frequency response. Using only three units of this novel EBG cell, a compact low-pass filter device has been fabricated, which achieved sharp cutoff and deep attenuation levels on the stop band. The measured results showed consistency with the simulation using the method of momentum (MoM).

  • 1441. Zou, Y. Z.
    et al.
    He, H. J.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analysis and optimization of an InGaAsP/InP waveguide variable optical attenuator2006In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 262, no 2, p. 188-192Article in journal (Refereed)
  • 1442. Zou, Yong-Zhuo
    et al.
    Lin, Zhi-Li
    Ling, Ti
    Yao, Jun
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A new broadband differential phase shifter fabricated using a novel CRLH structure2007In: Journal of Zhejiang University-Science A, ISSN 1673-565X, Vol. 8, no 10, p. 1568-1572Article in journal (Refereed)
  • 1443.
    Ängskog, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap.
    Avsiktliga elektromagnetiska störningar: Det osynliga hotet2014In: Electronics and the Environment, ISSN 1095-2020, Vol. 1, p. 16-17Article in journal (Other academic)
    Abstract [sv]

    I vårt moderna samhälle blir vi alltmer beroende av olika elektroniska kommunikations- och styrsystem, något som redan har upptäckts av kriminella, som utnyttjat svagheter i systemen för att begå brott. Detta är ett nytt scenario vi måste acceptera och lära oss hantera.

  • 1444.
    Ängskog, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap.
    EMP-symposium 8-9 maj 2014 i Oslo2014In: Electronic Environment, Vol. 2, p. 22-23Article in journal (Other (popular science, discussion, etc.))
  • 1445.
    Ängskog, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Högskolan i Gävle.
    Bäckström, Mats
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. SAAB Aeronautics, SAAB AB.
    Vallhagen, Bengt
    SAAB Aeronautics, SAAB AB.
    High Power Microwave Effects on Coated Window Panes2015In: Asia Electromagnetics Conference (ASIAEM) 2015, 2015Conference paper (Refereed)
    Abstract [en]

    Today window panes are usually coated with at least one metal or metal oxide layer to prevent heat energy of the light spectrum from propagating to the other side. This has given problems regarding radio propagation through windows, which might be utilized as a part of a buildings IEMI protection. This paper reports the results from measurements of the shielding effectiveness of a selection of modern window panes before and after irradiation with high power electromagnetic waves. The shielding effectiveness measurements are made in a nested reverberation chamber covering the range 1 – 18 GHz; both before and after high power irradiation at 1.3 GHz. The results show that the shielding effectiveness of window panes may be severely impaired due to thermal stress effects on the coatings during the irradiation, depending of the type of coating.

  • 1446.
    Ängskog, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Högskolan i Gävle.
    Bäckström, Mats
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. SAAB Aeronautics, SAAB AB.
    Vallhagen, Bengt
    SAAB Aeronautics, SAAB AB.
    Measurement of Radio Signal Propagation through Window Panes and Energy Saving Windows2015In: Proceedings of Electromagnetic Compatibility (EMC), 2015 IEEE International Symposium on, IEEE conference proceedings, 2015, p. 74-79Conference paper (Refereed)
    Abstract [en]

    Glass windows have undergone an energy saving evolution over the past three, four decades, from single panes till today’s ultralow-emission windows. While the earliest energy saving windows were constructed as a sandwich of clear glass panes using the vacuum-flask principle, modern low-emission windows includes panes with coatings of metal and/or metal oxides. This coating has caused radio propagation problems for communication systems; something that may be utilized to protect a building from intentional electromagnetic interference (IEMI) attacks and to help protecting against information leakage. In this paper measurements of the shielding performance of different generations of windows and qualities of window panes are presented. The intention is to include the results in a guide-line for IEMI protection of critical infrastructures. Measurements are made using two complementary methods; in a nested reverberation chamber and in a semi-anechoic chamber, both over the range 1 – 18 GHz. The results show a clear generation dependency where the energy saving windows largely do not attenuate RF signals at all and low-emission windows offer shielding effectiveness values between 10 and 45 dB with potentially as much as around 60 dB in the upper half of the spectrum.

  • 1447.
    Ängskog, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bäckström, Mats
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Vallhagen, Bengt
    Samuelsson, Carl
    Shielding Effectiveness of Energy Saving Windows and HPM Effects on Coated Window Panes Measurements Conducted 2014-2016-Results and Lessons Learned2016In: PROCEEDINGS OF THE 2016 INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC COMPATIBILITY - EMC EUROPE, IEEE conference proceedings, 2016, p. 461-466Conference paper (Refereed)
    Abstract [en]

    The past few decades have shown a veritable explosion of new versions of energy-saving windows and coated window panes. In the wake of this, problems with radio communications into and from within buildings has arisen. However, this unexpected attenuation of radio signals may also be used to shield a facility from incoming intentional electromagnetic interference (IEMI). With the intention to investigate the shielding effectiveness (SE) of modern windows and window panes a two-year measurement campaign was launched mid-2014. Another, little investigated area is what happens to coated glass when irradiated by a high-power microwave (HPM) source. Shielding effectiveness has been measured for different types of energy saving windows and coated window panes both in a semi-anechoic chamber and in a reverberation chamber over the frequency range 1-18 GHz. The effects of HPM irradiation were studied by comparing SE measured before and after the pulsed 28 kV/m L-band irradiation. The main conclusion is that with the right choice of window the shielding effectiveness of a building can reach up 40-50 dB. In this paper we summarize these measurements and lessons learned from the measurement campaign.

  • 1448.
    Ängskog, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap.
    Oakes, Ben
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Maintaining Functional Safety under an Intentional Electromagnetic Interference (IEMI) Attack2013Conference paper (Refereed)
    Abstract [en]

    The importance of protection against IEMI effects in civilian applications is growing rapidly as more and more societal infrastructure is equipped with electronic devices. This paper discusses methods to help maintaining functional safety in the event of an IEMI attack.

  • 1449.
    Ängskog, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Högskolan i Gävle.
    Ödman, Torbjörn
    SAAB Electronic Defence Systems, SAAB AB.
    Bäckström, Mats
    SAAB Aeronautics, SAAB AB.
    Vallhagen, Bengt
    SAAB Aeronautics, SAAB AB.
    Shielding Effectiveness Study of Two Fabrics with Microwave Properties Before and After High Power Irradiation2015In: Proceedings of the 2015 International Conference on Electromagnetics in Advanced Applications (ICEAA)ICEAA '15 - 17th Edition, IEEE conference proceedings, 2015, p. 930-933Conference paper (Refereed)
    Abstract [en]

    Over the past decade several applications forfabrics with electromagnetic properties have emerged, most ofthem relating to garments, including jackets with built-inantennas and workwear with increased radar visibility. Besidethese have surfaced two protective applications, namely toprotect transports of confidential equipment from discoveryand identification; and to protect sensitive apparatus fromdamage by high power electromagnetic irradiation e.g. in fieldoperations. In this paper results are presented frommeasurement of shielding effectiveness before and after highpower radiation for two types of fabrics under considerationfor the latter applications. Shielding effectivenessmeasurements have been conducted between 1 and 18 GHzwhile the high power irradiation

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