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Active Aperture

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Jiaru Chu – One of the best experts on this subject based on the ideXlab platform.

  • Double drive modes unimorph deformable mirror with high actuator count for astronomical application
    Proceedings of SPIE, 2014
    Co-Authors: Ying Liu, Junjie Chen, Jiaru Chu

    Abstract:

    Unimorph deformable mirrors are attrActive in adaptive optics system due to their advantages of simplicity, compact, low cost and large stroke. In this paper, a double drive modes unimorph deformable mirror is presented, which comprises a 200 μm thick PZT layer and a 400 μm thick silicon layer. This deformable has 214 inner actuators in the 50-mm Active Aperture, which are for the aberration correction and a outer ring actuator for generating an overall defocus bias. An analytical model based on the theory of plates and shells is built to predict the behavior of the deformable mirror. The stroke of the deformable mirror is tested in the experiments. In order to test the performance for aberration correction, the deformable mirror is used to correct the aberration from its imperfect initial mirror surface in the close-loop manner. The root-mean-square value of the mirror surface after the close-loop correction for ten iterations is about λ/40, which indicates this deformable mirror has a good aberration correction performance. This DM has the potential to be used for astronomical adaptive optics.

  • Low-cost unimorph deformable mirror with high actuator count for astronomical adaptive optics
    Optical Engineering, 2013
    Co-Authors: Ying Liu, Jiaru Chu

    Abstract:

    This paper presents a low-cost silicon unimorph deformable mirror (DM) that will be used for astronomical adaptive optics. The device has a simple construction consisting of a 400-μm-thick silicon wafer and a 200-μm-thick lead zirconate titanate film, with 214 actuators and 50-mm Active Aperture. The actuator displacement of the fabricated device is about 1 μm at 50 V. And the resonance frequency is 550 Hz. The simulation and experimental generation of Zernike mode shapes indicate that the fabricated DM has an excellent correction performance for both low order and high order aberrations.

  • Low-cost unimorph deformable mirror with high actuator count for astronomical adaptive optics
    Proceedings of SPIE, 2012
    Co-Authors: Ying Liu, Hao Rong, Jiaru Chu

    Abstract:

    This paper presents a low-cost silicon unimorph deformable mirror (DM) that will be used for astronomical adaptive optics. The device has a simple construction consisting of a 400-μm-thick silicon wafer and a 200-μm-thick lead zirconate titanate film, with 214 actuators and 50-mm Active Aperture. The actuator displacement of the fabricated device is about 1 μm at 50 V. And the resonance frequency is 550 Hz. The simula- tion and experimental generation of Zernike mode shapes indicate that the fabricated DM has an excellent correction performance for both low order and high order aberrations. © 2013 Society of Photo-Optical Instrumentation Engineers

Vladimir Pavlikov – One of the best experts on this subject based on the ideXlab platform.

  • Signal Processing Algorithm for Active Aperture Synthesis Systems
    2019 IEEE 15th International Conference on the Experience of Designing and Application of CAD Systems (CADSM), 2019
    Co-Authors: Vladimir Pavlikov, Valery Volosyuk, Simeon Zhyla, Anton Sobkolov

    Abstract:

    The real-time radar imaging of land cover over large areas is performed from aerospace carriers via imaging equipment operating in the optical, infrared and radio wavebands. The latter waveband allows to carry out the surveys regardless of weather and time of day. However, since radio waves are significantly longer (in comparison with optical and infrared ones), to achieve high-resolution images in spatial coordinates it is necessary to use antennas dozens, hundreds or even thousands of meters long. Naturally, it is rather difficult – and in most cases simply impossible – to implement this large antenna Aperture. Therefore, since the middle of the XX century, specially synthesized systems consisting one or several antennas, which can be repositioned according to a given law, has been widely used. Signals recorded in different areas of space are accumulated and then processed altogether. This creates the effect of using large antennas. In this case, there are two main methods of signal processing implemented, respectively, in Active radar systems with Aperture synthesis and passive Aperture synthesis systems. Traditionally, the viewing areas of these systems are correlated – the Active systems form images within the range of angles ±(15°-50°) from the nadir, and passive systems within ±15° from the nadir. The physical essence of the images obtained at the outputs of these systems is also different complicating the image formation within the entire region of ±50° from the nadir. This report combines the features of signal processing in Active and passive systems with the Aperture synthesis proposing a system of Active Aperture synthesis. This allows to obtain radar images of high resolution in spatial coordinates within the monitored area that cannot be viewed by Active radars, and the physical essence of the images themselves will be close to the essence of the images obtained by Active radar systems with synthesized Aperture.

  • Active Aperture Synthesis Radar for High Spatial Resolution Imaging
    2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS), 2018
    Co-Authors: Vladimir Pavlikov, Valery Volosyuk, Simeon Zhyla, Nguyen Van Huu

    Abstract:

    To solve problems of high-precision mapping of spatially extended objects regardless of weather conditions and time of day, radar imaging systems are used. The globality and efficiency of the survey is provided by the placement of radars on aerospace carriers. At the same time, there has been a proliferation of side-scan radars (providing a wide viewing range with a low spatial resolution) and antenna Aperture synthesis radars (these provide high resolution in spatial coordinates, which depends on the type of survey). Radars used for imaging are classified according to various characteristics determining their advantages and disadvantages. Among such features, we can also distinguish the radar viewing area, which is currently limited to angles of 15° to 60° to the right and left of the observation in the nadir. The viewing range from -15° to + 15° from the nadir is characterized by a low resolution in range and traditionally is not visible by these radars (the socalled “blind zone”). In this regard, an alternative system for building radar images from aerospace carriers is proposed. It will provide imaging with high angular resolution of the viewing range from -15° to + 15° from the nadir. The main feature of the developed radar lies in the signal processing algorithm that combines methods of Active (the presence of probing UWB signal) and passive (Aperture synthesis) radiolocation. In addition, the radar implements a new method of “spectral Aperture synthesis,” which allows the transition from processing of UWB signals with the continuum spectrum to processing multi-band signal processing.

  • UWB Active Aperture synthesis radar the operating principle and development of the radar block diagram
    2017 IEEE Microwaves Radar and Remote Sensing Symposium (MRRS), 2017
    Co-Authors: Vladimir Pavlikov, Valery Volosyuk, Semen Zhyla

    Abstract:

    The new algorithm of signal processing for building of high spatial resolution radar images is developed. A distinctive feature of this algorithm is the ability to form images of the area that is traditionally not viewable from aircraft and aerospace objects. This area approximates usually ±(20°…25°) from the aircraft’s normal axis. In this angle sector the horizontal range resolution of radar images is low. The block diagram of complex radio engineering system that combines advantages of Active radar and passive Aperture synthesis systems is developed for obtaining of images with the acceptable spatial coordinate resolution in the angle sectors of observation.

P.f. Wahid – One of the best experts on this subject based on the ideXlab platform.

  • A microwave Gaussian-beam launcher with an Active Aperture-blockage to control the spot-size of the beam
    IEEE Transactions on Microwave Theory and Techniques, 1994
    Co-Authors: C Gu, Perambur S P S Neelakanta, Varakorn Ungvichian, P.f. Wahid

    Abstract:

    A method of controlling the spot-size of a focused microwave Gaussian-beam using an Active Aperture-blockage is described. The Gaussian-beam launcher consists of an open-ended scalar-horn with a dielectric hyperhemisphere at its Aperture. Also included is an AgI-pellet at the Aperture-center with a provision to heat it with an external dc source. The scalar-horn plus the dielectric lens launch a Gaussian-beam; and, the AgI pellet when heated, becomes a superionic conductor offering an Aperture-blockage. This results in a variation of the spot-size of the emergent-beam. Theoretical results and experimental data are furnished and compared.