Mr. Varun Kumar Profile

Varun Kumar

Ph.D. Student at Indian Institute of Astrophysics

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Proceedings Article | 6 July 2018 Paper

Design considerations of an inductive sensor for segmented mirror telescopes

Varun Kumar, Padmakar Parihar, Athul Nakulan, Arjun Manoharan

Proceedings Volume 10700, 1070061 (2018) https://doi.org/10.1117/12.2313009

KEYWORDS: Sensors, Telescopes, Space telescopes, Segmented mirrors, Electronics, Inductance, Mirrors, Optical instrument design, Magnetism, 3D modeling

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The Segmented mirror technology has become natural choice for any optical telescope larger than 8 meter in size, where small mirror segments are aligned and positioned with respect to each other to an accuracy of few tens of nanometer. Primary mirror control system with the help of edge sensor and soft linear actuator maintains that alignment which changes due to gravity and wind loading. For any segmented mirror telescope edge-sensor plays very critical role. It should have very high spatial resolution (few nanometer), large range, multidimensional sensing, high temporal stability as well as immunity towards relative change in temperature and humidity. Though capacitive sensors are widely used for this purpose, however, their inherent sensitivity towards humidity and dust make them unsuitable for telescopes operating at humid low altitude regions. Whereas, inductance based sensors, working on the principal of mutual inductance variation between two planar inductor coils, produce promising results in such a situation. Looking at stringent requirements, design and development of a planar inductive sensor is a challenge. As a first step toward sensor development, we have explored the design aspects of it. The inductive coils are first simulated and analyzed using electromagnetic FEA software for different coil parameters. The design considerations include optimization of coil parameters such as geometry of coils, trace densities, number of turns, etc. and operational requirements such as number of degree of freedoms to be sensed, range of travel, spatial resolution, as well as required sensitivity. The simulation results are also verified through experimentation. In this first paper we report the design and analysis results obtained from FEA simulations.

Proceedings Article | 6 July 2018 Presentation + Paper

Prototype segmented mirror telescope: a pathfinder of India's Large Optical-NIR telescope project

Padmakar Parihar, Prasanna Deshmukh, Annu Jacob, Varun Kumar, Abhishek Goudar, S. Sriram, S. Nagabhusan, S. Amitkumar, K. V. Govinda, D. S. Sandeep, P. M. M. Kemkar, G. C. Anupama

Proceedings Volume 10700, 107001A (2018) https://doi.org/10.1117/12.2313079

KEYWORDS: Mirrors, Telescopes, Sensors, Actuators, Segmented mirrors, Prototyping, Optical instrument design

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To cater the need of growing astronomical community of India, there is a proposal to install 10-12m size optical-NIR telescope, equipped with state of the art back-end instruments . A telescope of this size is possible only, when primary mirror is made of smaller mirror segments. In order to get acquainted with segmented mirror telescope technology, at Indian Institute of Astrophysics Bangalore, we have initiated a project to develop a small prototype telescope made of small mirror segments. The proposed prototype telescope will use seven hexagonal mirrors, which will be supported by simple mirror support assembly and driven by indigenously developed voice coil based actuators. We also plan to make use of in-house developed inexpensive inductive edge sensor, which can precisely sense inter-segment relative displacement. The telescope mount is supposed to be Alt-Az and secondary mirror will be supported by trusses made of steel. The primary axes like elevation, azimuth and field de-rotator will be driven by direct drive motors. Though the primary objective of this telescope is to demonstrate the segmented mirror technology, however, we have designed the telescope in such way that it can also be used to a few dedicated science cases. The telescope is planned to be installed at Hanle, Ladakh India which is also a potential site for India's large telescope project. In this paper, we will present the progress made in opto-mechanical design as well development of other sub-systems required for the PSMT. The prototyping effort is one step toward realization of a large telescope in India and it is expected to be completed in two years period.

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