The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform

Daomu Zhao - One of the best experts on this subject based on the ideXlab platform.

  • Random sources generating hollow Array beams
    Optics express, 2020
    Co-Authors: Keming Pan, Daomu Zhao
    Abstract:

    A novel class of partially coherent light sources that can yield stable optical lattice termed hollow Array in the far field is introduced. The Array Dimension, the distance of hollow lobes intensity profile, the size and shape of the inner and outer lobe contours and other features can be flexibly controlled by altering the source parameters. Further, every lobe can be shaped with polar and Cartesian symmetry and even combined to form nested structures. The applications of the work are envisioned in material surface processing and particle trapping.

  • Random medium model for producing optical coherence lattice
    Optics express, 2017
    Co-Authors: Yi Ding, Daomu Zhao
    Abstract:

    Within the Markov approximation, we introduce a novel class of random media which can produce a scattered field with optical lattice patterns. It is shown that the Array Dimension, lobes intensity profile, and the periodicity of the optical lattice can be flexibly controlled by altering the correlation parameters of scattering potential of the random medium. In addition, a new method for designing random media is proposed. It is shown that the convolution of any two legitimate degrees of potential correlation can lead to a new degree of potential correlation corresponding to a new scattered intensity distribution. An example of a novel family of random media is cited to demonstrate the result.

  • Gaussian Schell-model Arrays.
    Optics letters, 2015
    Co-Authors: Zhangrong Mei, Daomu Zhao, Olga Korotkova, Yonghua Mao
    Abstract:

    We introduce a novel class of planar, quasi-homogeneous Schell-model source for producing far fields with optical lattice average intensity patterns and derive the corresponding beam conditions. The Array Dimension, lobes intensity profile, and periodicity of the optical lattice can be flexibly tuned by changing the correlation parameters of the source field. It is also found that, with an appropriate choice of the source parameters, the radiant intensity may possess flat-topped intensity patterns.

Lorenz-peter Schmidt - One of the best experts on this subject based on the ideXlab platform.

  • Millimeter-wave imaging with optimized sparse periodic Array for short-range applications
    IEEE Transactions on Geoscience and Remote Sensing, 2011
    Co-Authors: Frank Gumbmann, Lorenz-peter Schmidt
    Abstract:

    This paper presents a multiple-input–multiple-output imaging system on the basis of a hybrid concept with synthetic aperture radar and digital beam forming. By moving a multistatic linear Array perpendicularly to the Array Dimension, a 2-D aperture is sampled. The scope of application is concealed weapon detection in conjunction with the imaging of humans and, alternatively, nondestructive testing (NDT). The frequency range of 75–90 GHz was chosen because of the inherent high lateral resolution. For NDT, it seems to be a good compromise between lateral resolution and penetration depth as well. A moderate number of transmit and receive channels are achieved by a sparse periodic Array (SPA) design. Since this is a far-field approach, ambiguities are not well suppressed in the near-field point spread function of the sparse Array. An extension of the SPA concept for short-range applications on the basis of an optimized Array design and an optimized beamforming algorithm is presented in this paper.

  • Sparse linear Array design for a short range imaging radar
    2009
    Co-Authors: Frank Gumbmann, Phat Tran, Lorenz-peter Schmidt
    Abstract:

    This paper presents the design of an active short range imaging system in the Ka-band (26.6 – 40 GHz). The sensor is a multistatic linear Array which is moved perpendicular to the Array Dimension for the purpose of 3D imaging. By sequentially switching on the transmitters and simultaneous reception of the scattered field by each receiver, a fast sampling of the 2D aperture plane is achieved. To reduce the number of parallel receive channels, a thinned Array on the base of sparse periodic Arrays (SPA) was developed. Due to non focussing antenna elements, numerical reconstruction algorithms, for near field conditions, have to be applied for a high lateral resolution. First simulation results verify the imaging quality of this concept and the functionality of the proposed reconstruction algorithm.

  • Multistatic Short Range Ka-Band Imaging System
    2009 German Microwave Conference, 2009
    Co-Authors: Frank Gumbmann, Phat Tran, Jochen Weinzierl, Lorenz-peter Schmidt
    Abstract:

    This paper presents the concept of a Ka-Band (26.5 - 40 GHz) multistatic active short range imaging system. The motivation for this work was the development of a fast scanning imaging system for non destructive testing (NDT) or security scenarios. The goal was to derive a 3D reconstruction of the device under test (DUT). The imaging system consists of a linear receive Array and spatially distributed transmitters with non focussing antenna elements. This transmit/receive Array is moved perpendicular to the Array Dimension. By switching between each transmitter and simultaneous reception of the scattered field by each receiver, a fast sampling of the 2D aperture plane is achieved. Due to unfocussed antenna elements numerical reconstruction algorithms have to be applied for a highT lateral resolution. An aperture synthesis concept is presented to reconstruct the raw data. It is based on the separation of the reconstruction kernel into a horizontal and a vertical part. Range resolution is achieved by a broadband stepped frequency continuous wave (SFCW) radar. In order demonstrate the efficiency of the new reconstruction kernel first results are demonstrated with simulated and measured data.

Chen A-lei - One of the best experts on this subject based on the ideXlab platform.

  • An Array model based on time-domain imaging for wideband MIMO radar
    Signal Processing, 2011
    Co-Authors: Chen A-lei
    Abstract:

    Multiple-input and multiple-output(MIMO) radar is a new radar system developed in recent years.In order to reduce the Array Dimension and hardware complexity,and make the application of MIMO radar imaging technology come true,a nonlinear Array model is proposed,combined with the improved back-projection(BP) imaging algorithm.The proposed Array model can acquire the Array element intervals by the cross-range resolution requirement of imaging system and the choice of the imaging scene,and so can reduce evidently the Array Dimension and hardware complexity.Meanwhile,the application of time-domain imaging algorithm can avoid the limitation of sampling theory in frequency-domain,make the Array design become flexible,and furthermore reduce the Array Dimension and hardware complexity.Simulation experiments show the correctness and effectiveness of this Array model.

Frank Gumbmann - One of the best experts on this subject based on the ideXlab platform.

  • Millimeter-wave imaging with optimized sparse periodic Array for short-range applications
    IEEE Transactions on Geoscience and Remote Sensing, 2011
    Co-Authors: Frank Gumbmann, Lorenz-peter Schmidt
    Abstract:

    This paper presents a multiple-input–multiple-output imaging system on the basis of a hybrid concept with synthetic aperture radar and digital beam forming. By moving a multistatic linear Array perpendicularly to the Array Dimension, a 2-D aperture is sampled. The scope of application is concealed weapon detection in conjunction with the imaging of humans and, alternatively, nondestructive testing (NDT). The frequency range of 75–90 GHz was chosen because of the inherent high lateral resolution. For NDT, it seems to be a good compromise between lateral resolution and penetration depth as well. A moderate number of transmit and receive channels are achieved by a sparse periodic Array (SPA) design. Since this is a far-field approach, ambiguities are not well suppressed in the near-field point spread function of the sparse Array. An extension of the SPA concept for short-range applications on the basis of an optimized Array design and an optimized beamforming algorithm is presented in this paper.

  • Sparse linear Array design for a short range imaging radar
    2009
    Co-Authors: Frank Gumbmann, Phat Tran, Lorenz-peter Schmidt
    Abstract:

    This paper presents the design of an active short range imaging system in the Ka-band (26.6 – 40 GHz). The sensor is a multistatic linear Array which is moved perpendicular to the Array Dimension for the purpose of 3D imaging. By sequentially switching on the transmitters and simultaneous reception of the scattered field by each receiver, a fast sampling of the 2D aperture plane is achieved. To reduce the number of parallel receive channels, a thinned Array on the base of sparse periodic Arrays (SPA) was developed. Due to non focussing antenna elements, numerical reconstruction algorithms, for near field conditions, have to be applied for a high lateral resolution. First simulation results verify the imaging quality of this concept and the functionality of the proposed reconstruction algorithm.

  • Multistatic Short Range Ka-Band Imaging System
    2009 German Microwave Conference, 2009
    Co-Authors: Frank Gumbmann, Phat Tran, Jochen Weinzierl, Lorenz-peter Schmidt
    Abstract:

    This paper presents the concept of a Ka-Band (26.5 - 40 GHz) multistatic active short range imaging system. The motivation for this work was the development of a fast scanning imaging system for non destructive testing (NDT) or security scenarios. The goal was to derive a 3D reconstruction of the device under test (DUT). The imaging system consists of a linear receive Array and spatially distributed transmitters with non focussing antenna elements. This transmit/receive Array is moved perpendicular to the Array Dimension. By switching between each transmitter and simultaneous reception of the scattered field by each receiver, a fast sampling of the 2D aperture plane is achieved. Due to unfocussed antenna elements numerical reconstruction algorithms have to be applied for a highT lateral resolution. An aperture synthesis concept is presented to reconstruct the raw data. It is based on the separation of the reconstruction kernel into a horizontal and a vertical part. Range resolution is achieved by a broadband stepped frequency continuous wave (SFCW) radar. In order demonstrate the efficiency of the new reconstruction kernel first results are demonstrated with simulated and measured data.

Seppo Valkealahti - One of the best experts on this subject based on the ideXlab platform.

  • output power variation of different pv Array configurations during irradiance transitions caused by moving clouds
    Applied Energy, 2017
    Co-Authors: Kari Lappalainen, Seppo Valkealahti
    Abstract:

    Abstract This paper presents a study of the output power variation of different photovoltaic (PV) Array configurations during irradiance transitions caused by moving clouds. The study was based on velocity and other characteristics of roughly 27,000 irradiance transitions identified in measured irradiance data and conducted using a mathematical model of irradiance transitions and an experimentally verified simulation model of a PV module. The studied electrical PV Array configurations were series-parallel, total-cross-tied and multi-string. The different PV Array orientations and layouts (physical shapes) of the configurations were also studied. The average rate of change of the power of these studied PV Array configurations during the irradiance transitions was around 3%/s and the maximum instantaneous rates of change of the power were around 75%/s. Half of the time during the studied transitions, the rate of change in the power was over 1.2%/s, and most of the time during the transitions, it exceeded typical PV power ramp rate limits set by grid operators. The average rate of change of PV Array power decreased with an increasing maximum Array Dimension and it was observed to be the largest when the shorter Dimension of the Array was parallel to the dominant movement direction of the shadow edges. The results of this study are relevant especially in terms of PV Array design, maximum power point tracking algorithm development and energy storage systems sizing.