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Paul Chow - One of the best experts on this subject based on the ideXlab platform.

  • A theoretical study of terahertz surface plasmons on a cylindrical Metal Wire
    Physics of Plasmas, 2017
    Co-Authors: Kwo Ray Chu, Paul Chow
    Abstract:

    This study addresses some theoretical issues of interest to surface plasmon propagation along a Metal-Wire waveguide at terahertz (THz) frequencies. The conductor is characterized by a shallow field penetration depth at microwave frequencies and the transparency to frequencies above the ultraviolet. Falling between these two regimes, THz surface plasmons are thus particularly sensitive to the electron dynamics in the Metal Wire. Also, with evanescent fields both inside and outside, surface plasmons are known to be loosely bound to the Metal Wire, which further complicates the behavior of surface plasmons. These issues are examined here in a comparative study under AC- and DC-conductivity models. Depending on the Wire radius, the frequency dependence of the conductivity has either a very significant effect on the Ohmic loss or no effect at all, while an opposite trend is found for the wave attenuation rate. Extensive data on the wave attenuation constant is also presented and interpreted. The results show ...

Bengt Lennartson - One of the best experts on this subject based on the ideXlab platform.

  • Resistance measurements for control of laser Metal Wire deposition
    Optics and Lasers in Engineering, 2014
    Co-Authors: Petter Hagqvist, Almir Heralic, Anna-karin Christiansson, Bengt Lennartson
    Abstract:

    A method for controlling robotized laser Metal Wire deposition on-line by electrical resistance metering is proposed. The concept of measuring the combined resistance of the Wire and the weld pool is introduced and evaluated for automatic control purposes. Droplet formation, detachment of the Wire from the weld pool and stubbing can be hard to avoid during processing due to the sensitive process and short reaction times needed for making on-line adjustments. The implemented system shows a possible route for automatic control of the process wherein such problems can be avoided automatically. The method proves to successfully adjust the distance between the tool and the workpiece through controlling the robot height position, thus increasing stability of the laser Metal Wire deposition process. (C) 2013 Elsevier Ltd. All rights reserved.

  • increased stability in laser Metal Wire deposition through feedback from optical measurements
    Optics and Lasers in Engineering, 2010
    Co-Authors: Almir Heralic, Anna-karin Christiansson, Mattias Ottosson, Bengt Lennartson
    Abstract:

    Robotized laser Metal-Wire deposition is a fairly new technique being developed at University West in cooperation with Swedish industry for solid freeform fabrication of fully densed Metal structures. It is developed around a standard welding cell and uses robotized fiber laser welding and Wire filler material together with a layered manufacturing method to create Metal structures. In this work a monitoring system, comprising two cameras and a projected laser line, is developed for on-line control of the deposition process. The controller is a combination of a PI-controller for the bead width and a feed-forward compensator for the bead height. It is evaluated through deposition of single-bead walls, and the results show that the process stability is improved when the proposed controller is used. (C) 2009 Elsevier Ltd. All rights reserved.

  • Control Design for Automation of Robotized Laser Metal-Wire Deposition
    IFAC Proceedings Volumes, 2008
    Co-Authors: Almir Heralic, Anna-karin Christiansson, Kjell Hurtig, Mattias Ottosson, Bengt Lennartson
    Abstract:

    In this paper a novel approach towards automation of robotized laser Metal-Wire deposition (RLMwD) is described. The RLMwD technique is being developed at University West in cooperation with Swedis ...

  • Automation of robotized laser Metal-Wire deposition
    2007
    Co-Authors: Almir Heralic, Anna-karin Christiansson, Kjell Hurtig, Mattias Ottosson, Bengt Lennartson
    Abstract:

    Robotized Laser Metal-Wire Deposition (RLMwD) is a novel technique for solid freeform fabrication of fully-dense Metal structures. The process utilizes robotized fibre laser welding and Wire filler material together with a layered manufacturing method to create Metal structures directly from a CAD drawing. RLMwD can also be used for repairing or modifying existing components. Since a 6-axis robot arm manoeuvres the welding tool, a higher level of flexibility is introduced compared to most existing commercial Metal deposition systems. Also, introducing Metal Wire as filler material, rather than Metal powder, we expect to increase the manufacturing rate considerably and to improve the Metallurgical properties of the built-up components. Initially, tool-steel and nickel based alloys will be considered. The main objective of this research is the automation of the deposition process. For this purpose a system has been developed at University West for measuring crucial signals during deposition. It monitors the variations in the process parameters, the built geometry, and the temperature, before and after a new layer is produced and can thereby facilitate for automatic compensation. In this paper the structure of the RLMwD system is described, including a control strategy for automation of the deposition process.

Shunsuke Inoue - One of the best experts on this subject based on the ideXlab platform.

  • strong sub terahertz surface waves generated on a Metal Wire by high intensity laser pulses
    Scientific Reports, 2015
    Co-Authors: Shigeki Tokita, Shuji Sakabe, Takeshi Nagashima, Masaki Hashida, Shunsuke Inoue
    Abstract:

    Terahertz pulses trapped as surface waves on a Wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a Wire waveguide remains a challenge. Here, ultrafast field propagation along a Metal Wire driven by a femtosecond laser pulse with an intensity of 1018 W/cm2 is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the Wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200 MV/m and 7 ps, respectively.

Kwo Ray Chu - One of the best experts on this subject based on the ideXlab platform.

  • A theoretical study of terahertz surface plasmons on a cylindrical Metal Wire
    Physics of Plasmas, 2017
    Co-Authors: Kwo Ray Chu, Paul Chow
    Abstract:

    This study addresses some theoretical issues of interest to surface plasmon propagation along a Metal-Wire waveguide at terahertz (THz) frequencies. The conductor is characterized by a shallow field penetration depth at microwave frequencies and the transparency to frequencies above the ultraviolet. Falling between these two regimes, THz surface plasmons are thus particularly sensitive to the electron dynamics in the Metal Wire. Also, with evanescent fields both inside and outside, surface plasmons are known to be loosely bound to the Metal Wire, which further complicates the behavior of surface plasmons. These issues are examined here in a comparative study under AC- and DC-conductivity models. Depending on the Wire radius, the frequency dependence of the conductivity has either a very significant effect on the Ohmic loss or no effect at all, while an opposite trend is found for the wave attenuation rate. Extensive data on the wave attenuation constant is also presented and interpreted. The results show ...

Almir Heralic - One of the best experts on this subject based on the ideXlab platform.

  • Resistance measurements for control of laser Metal Wire deposition
    Optics and Lasers in Engineering, 2014
    Co-Authors: Petter Hagqvist, Almir Heralic, Anna-karin Christiansson, Bengt Lennartson
    Abstract:

    A method for controlling robotized laser Metal Wire deposition on-line by electrical resistance metering is proposed. The concept of measuring the combined resistance of the Wire and the weld pool is introduced and evaluated for automatic control purposes. Droplet formation, detachment of the Wire from the weld pool and stubbing can be hard to avoid during processing due to the sensitive process and short reaction times needed for making on-line adjustments. The implemented system shows a possible route for automatic control of the process wherein such problems can be avoided automatically. The method proves to successfully adjust the distance between the tool and the workpiece through controlling the robot height position, thus increasing stability of the laser Metal Wire deposition process. (C) 2013 Elsevier Ltd. All rights reserved.

  • increased stability in laser Metal Wire deposition through feedback from optical measurements
    Optics and Lasers in Engineering, 2010
    Co-Authors: Almir Heralic, Anna-karin Christiansson, Mattias Ottosson, Bengt Lennartson
    Abstract:

    Robotized laser Metal-Wire deposition is a fairly new technique being developed at University West in cooperation with Swedish industry for solid freeform fabrication of fully densed Metal structures. It is developed around a standard welding cell and uses robotized fiber laser welding and Wire filler material together with a layered manufacturing method to create Metal structures. In this work a monitoring system, comprising two cameras and a projected laser line, is developed for on-line control of the deposition process. The controller is a combination of a PI-controller for the bead width and a feed-forward compensator for the bead height. It is evaluated through deposition of single-bead walls, and the results show that the process stability is improved when the proposed controller is used. (C) 2009 Elsevier Ltd. All rights reserved.

  • Control Design for Automation of Robotized Laser Metal-Wire Deposition
    IFAC Proceedings Volumes, 2008
    Co-Authors: Almir Heralic, Anna-karin Christiansson, Kjell Hurtig, Mattias Ottosson, Bengt Lennartson
    Abstract:

    In this paper a novel approach towards automation of robotized laser Metal-Wire deposition (RLMwD) is described. The RLMwD technique is being developed at University West in cooperation with Swedis ...

  • Automation of robotized laser Metal-Wire deposition
    2007
    Co-Authors: Almir Heralic, Anna-karin Christiansson, Kjell Hurtig, Mattias Ottosson, Bengt Lennartson
    Abstract:

    Robotized Laser Metal-Wire Deposition (RLMwD) is a novel technique for solid freeform fabrication of fully-dense Metal structures. The process utilizes robotized fibre laser welding and Wire filler material together with a layered manufacturing method to create Metal structures directly from a CAD drawing. RLMwD can also be used for repairing or modifying existing components. Since a 6-axis robot arm manoeuvres the welding tool, a higher level of flexibility is introduced compared to most existing commercial Metal deposition systems. Also, introducing Metal Wire as filler material, rather than Metal powder, we expect to increase the manufacturing rate considerably and to improve the Metallurgical properties of the built-up components. Initially, tool-steel and nickel based alloys will be considered. The main objective of this research is the automation of the deposition process. For this purpose a system has been developed at University West for measuring crucial signals during deposition. It monitors the variations in the process parameters, the built geometry, and the temperature, before and after a new layer is produced and can thereby facilitate for automatic compensation. In this paper the structure of the RLMwD system is described, including a control strategy for automation of the deposition process.