The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Jiaru Chu - One of the best experts on this subject based on the ideXlab platform.
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Double drive modes unimorph deformable mirror with high actuator count for astronomical application
Proceedings of SPIE, 2014Co-Authors: Ying Liu, Junjie Chen, Jiaru ChuAbstract: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.
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Low-cost unimorph deformable mirror with high actuator count for astronomical adaptive optics
Optical Engineering, 2013Co-Authors: Ying Liu, Jiaru ChuAbstract: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.
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Low-cost unimorph deformable mirror with high actuator count for astronomical adaptive optics
Proceedings of SPIE, 2012Co-Authors: Ying Liu, Hao Rong, Jiaru ChuAbstract: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.
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Signal Processing Algorithm for Active Aperture Synthesis Systems
2019 IEEE 15th International Conference on the Experience of Designing and Application of CAD Systems (CADSM), 2019Co-Authors: Vladimir Pavlikov, Valery Volosyuk, Simeon Zhyla, Anton SobkolovAbstract: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.
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Active Aperture Synthesis Radar for High Spatial Resolution Imaging
2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS), 2018Co-Authors: Vladimir Pavlikov, Valery Volosyuk, Simeon Zhyla, Nguyen Van HuuAbstract: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.
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UWB Active Aperture synthesis radar the operating principle and development of the radar block diagram
2017 IEEE Microwaves Radar and Remote Sensing Symposium (MRRS), 2017Co-Authors: Vladimir Pavlikov, Valery Volosyuk, Semen ZhylaAbstract: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.
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A new method of multi-frequency Active Aperture synthesis for imaging of SAR blind zone under aerospace vehicle
2017 14th International Conference The Experience of Designing and Application of CAD Systems in Microelectronics (CADSM), 2017Co-Authors: Vladimir Pavlikov, Valery Volosyuk, Semen Zhyla, Huu Nguyen Van, Kiem Nguyen VanAbstract:New method of radar imaging from aerospace carriers is proposing. The method allows to obtain the radar images with high spatial resolution of surface area in the angle range of ±25° from normal aircraft axis. This area is traditionally doesn't map due to the lack of the range resolution in this observation sector of angles. Method assumes the irradiation of the underlying surface by the multifrequency signal and a subsequent space-time processing of the reflected signals in the Aperture synthesis system. In contrast to the Aperture synthesis systems used in radio astronomy and remote sensing, signal processing is performed under parametric a priori uncertainty.
P.f. Wahid - One of the best experts on this subject based on the ideXlab platform.
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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, 1994Co-Authors: C Gu, Perambur S P S Neelakanta, Varakorn Ungvichian, P.f. WahidAbstract: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.
Paul Bierden - One of the best experts on this subject based on the ideXlab platform.
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Performance analysis of two high actuator count MEMS deformable mirrors
MEMS Adaptive Optics VII, 2013Co-Authors: Peter Ryan, Steven Cornelissen, Charlie V. Lam, Paul BierdenAbstract:Two new MEMS deformable mirrors have been designed and fabricated, one having a continuous facesheet with an Active Aperture of 20mm and 2040 actuators and the other, a similarly sized segmented tip tilt piston DM containing 1021 elements and 3063 actuators. The surface figures, electro mechanical performances, and actuator yield of these devices, with statistical information, are reported here. The statistical distributions of these measurements directly illustrate the surface variance of Boston Micromachines deformable mirrors. Measurements of the surface figure were also performed with the elements at different actuation states. Also presented here are deviations of the surface figure under actuation versus at its rest state, the electromechanical distribution, and a dynamic analysis.
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MEMS Deformable Mirrors for Astronomical Adaptive Optics
Proceedings of SPIE, 2010Co-Authors: Steven Cornelissen, Thomas G. Bifano, Allyson L. Hartzell, Jason B. Stewart, Paul BierdenAbstract:We report on the development of high actuator count, micro-electromechanical (MEMS) deformable mirrors designed for high order wavefront correction in ground and space-based astronomical adaptive optics instruments. The design of these polysilicon, surface-micromachined MEMS deformable mirrors builds on technology that has been used extensively to correct for ocular aberrations in retinal imaging systems and for compensation of atmospheric turbulence in free-space laser communication. These light-weight, low power deformable mirrors have an Active Aperture of up to 25.2mm consisting of a thin silicon membrane mirror supported by an array of 140 to 4092 electrostatic actuators which exhibit no hysteresis and have sub-nanometer repeatability making them well suited for open-loop control applications such as Multi-Object Adaptive Optics (MOAO). The continuous membrane deformable mirrors, coated with a highly reflective metal film, are capable of up to 6μm of stroke, have a surface finish of
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MEMS deformable mirrors in astronomical adaptive optics
1st AO4ELT conference - Adaptive Optics for Extremely Large Telescopes, 2010Co-Authors: Thomas G. Bifano, Steven Cornelissen, Paul BierdenAbstract:We report on the development of microelectromechanical (MEMS) deformable mirrors designed for ground and space-based astronomical instruments using adaptive optics. These light-weight, low power deformable mirrors will have an Active Aperture of up to 25.2mm consisting of thin silicon membrane mirror supported by an array of up to 4096 electrostatic actuators exhibiting no hysteresis and sub-nanometer repeatability. The continuous membrane deformable mirrors, coated with a highly reflective metal film, are capable of up to 4µm of stroke, have a surface finish of
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Development of a 4096 element MEMS continuous membrane deformable mirror for high contrast astronomical imaging
Proceedings of SPIE, 2006Co-Authors: Steven Cornelissen, Paul Bierden, Thomas G. BifanoAbstract:Presented in this paper is the development of a 4096 element continuous membrane deformable mirror under development for the Gemini Planet Imaging instrument designed for extra solar planet detection. This deformable mirror will enable the next generation of adaptive optics ("Extreme" AO) capable of achieving contrasts of up to 10 8 , required to detect these planets that are obscured by the brightness of its parent star. This surface micromachined MEMS deformable mirror will have an Active Aperture of 25.2mm consisting of thin silicon membrane mirror supported by an array of 64x64 electrostatic actuators exhibiting no hysteresis and sub-nanometer repeatability. This deformable mirror will be capable of 4μm of stroke, have a surface finish of
Gregory N. Washington - One of the best experts on this subject based on the ideXlab platform.
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Design and Construction of a Piezoelectric Point Actuated Active Aperture Antenna
Journal of Intelligent Material Systems and Structures, 2002Co-Authors: Marc R. Angelino, Gregory N. WashingtonAbstract:In this research, an antenna's far field radiation pattern is controlled by controlling the shape of a sub reflector in a Cassegrain antenna system. The antenna is actuated using multiple point actuators in contact with the reflector surface. A lead zircamate titanate (PZT) stack coupled with a friction-based compliant mechanism gives the point actuators used in this design an advantage over similar studies using PZT bimorph or PVDF actuators. The main advantage stems from the fact that the displacement can be maintained without the continuous application of voltage. An electromechanical model is used to describe the motion of the stack, and the friction based compliant mechanism is modeled similar to power screw-type actuators. A combined finite element-electromagnetic analysis code is used to determine the desired shape of the reflector and the corresponding actuator displacements. The final shape of the reflector is verified using stereo photogrammetry.
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Independent Modal Sliding Mode Shape and Vibration Control Using a Stereophotogrammetric Measurement System
Adaptive Structures and Materials Systems, 2002Co-Authors: Sivasubramaniam Manthram, Gregory N. WashingtonAbstract:The last decade has seen the advent of Active Aperture antennas and other large distributed parameter systems. These antennas have the capability to change their shape to resemble a desired radiation pattern. In this study a method to simultaneously achieve Active shape and vibration control of distributed parameter systems is presented. The optimal actuator location is computed for a desired profile using non-linear optimal programming techniques. For most shape control applications the actuator and sensor dynamics are much faster than the structural dynamics and slow shape changes are sufficient, thus quasi-static analysis is sufficient. The quasi-static actuation forces for the desired profile are then calculated by using independent modal space control (IMSC) principles. Quasi-static shape control is then implemented in a closed loop control using a 3-D photogrammetry sensing system. A sliding mode controller is designed for each dominant mode such that it drives the error between the required and actual modal contribution to zero. Conventional sliding mode controllers are discontinuous in nature and they might cause “control spillover”. This is avoided by using an “observer-based” solution.Copyright © 2002 by ASME
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Modeling and Control of a Singly Curved Active Aperture Antenna Using Curved Piezoceramic Actuators
Journal of Intelligent Material Systems and Structures, 2000Co-Authors: Richard Granger, Gregory N. Washington, Seung-keon KwakAbstract:There is an increasing need for Aperture antenna devices that incorporate multifunctional capability. One popular solution to this problem is the use of an Active Aperture antenna that is able to vary the direction and shape of its radiation pattern by using actuators to alter the shape of the reflector. This study focuses on the use of a pre-curved piezoceramic actuator, referred to as a THUNDER actuator, to change the shape of a prototype reflector. These actuators offer greater force, deflection and higher strength than traditional PZT actuators, while maintaining cost effectiveness. In this study the design of a prototype antenna structure that can accommodate deflection experiments and far-field radiation pattern tests is presented. The theoretical relationship between the dish deflection and the input voltage is established in two stages. In the first stage, the deflection at the end of the actuator is determined using a combination of Hamilton's principle and laminated composite curved beam theory. The piezoelectric properties of the actuator are also considered during this stage. In the second stage, the deflection at the tip of the dish is calculated using geometric relationships, with the assumption that the remaining portion of the dish moves as a rigid body. The resulting deflection equations yield results that closely match the experimental quasi-static deflection results for a given input voltage, despite the presence of hysteresis. A dynamic model for a THUNDER actuator is developed based on experimental frequency response measurements. Positive Positioned Feedback (PPF) control is implemented on the system, in order to reduce position overshoot and oscillations in the transient response of the structure. The controller yields an improvement in the transient response in both simulation and experiments. Finally, the controlled system is utilized to transmit radiation in the far field.
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Aperture antenna shape prediction by feedforward neural networks
IEEE Transactions on Antennas and Propagation, 1997Co-Authors: Gregory N. WashingtonAbstract:The emergence of adaptive "smart" materials has led to the design of Active Aperture antennas. Inherent in these antennas is the ability to change their shape in real time to meet various performance characteristics. When examining the usefulness of these antennas, one of the primary concerns is the antenna shape needed for a particular radiation pattern. Aperture antenna shape prediction is also a concern in the industrial production of semi-paraboloidal antennas. The work in this study employs an artificial neural network to model the Aperture antenna shape in real time. To test the accuracy of the network, the "threefold holdout technique" was employed. In this technique, sets of examples are "held out" of the training process and used to obtain the "true error" of the network. The network accurately predicted the Aperture shape exactly, to within three significant digits, 96% of the time.
