Mr. Prashanth Ramesh Profile

Prashanth Ramesh

at Ohio State Univ

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Publications (2)

Proceedings Article | 10 April 2010 Paper

Distributed intelligence using gallium nitride based active devices

Prashanth Ramesh, Sriram Krishnamoorthy, Pil Sung Park, Siddharth Rajan, Gregory Washington

Proceedings Volume 7643, 76431W (2010) https://doi.org/10.1117/12.847919

KEYWORDS: Gallium nitride, Etching, Electrodes, Waveguides, Semiconductors, Ultraviolet radiation, Metals, Semiconducting wafers, Intelligence systems, Optical switching

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Proceedings Article | 1 April 2009 Paper

Analysis and design of ferroelectric-based smart antenna structures

Prashanth Ramesh, Gregory Washington

Proceedings Volume 7291, 729110 (2009) https://doi.org/10.1117/12.816411

KEYWORDS: Antennas, Dielectrics, Microwave radiation, Data modeling, Ferroelectric materials, Systems modeling, Electro optical modeling, Dielectric polarization, Thermodynamics, Thin films

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Ferroelectrics in microwave antenna systems offer benefits of electronic tunability, compact size and light weight, speed of operation, high power-handling, low dc power consumption, and potential for low loss and cost. Ferroelectrics allow for the tuning of microwave devices by virtue of the nonlinear dependence of their dielectric permittivity on an applied electric field. Experiments on the field-polarization dependence of ferroelectric thin films show variation in dielectric permittivity of up to 50%. This is in contrast to the conventional dielectric materials used in electrical devices which have a relatively constant permittivity, indicative of the linear field-polarization curve. Ferroelectrics, with their variable dielectric constant introduce greater flexibility in correction and control of beam shapes and beam direction of antenna structures. The motivation behind this research is applying ferroelectrics to mechanical load bearing antenna structures, but in order to develop such structures, we need to understand not just the field-permittivity dependence, but also the coupled electro-thermo-mechanical behavior of ferroelectrics. In this paper, two models are discussed: a nonlinear phenomenological model relating the applied fields, strains and temperature to the dielectric permittivity based on the Devonshire thermodynamic framework, and a phenomenological model relating applied fields and temperature to the dielectric loss tangent. The models attempt to integrate the observed field-permittivity, strain-permittivity and temperature-permittivity behavior into one single unified model and extend the resulting model to better fit experimental data. Promising matches with experimental data are obtained. These relations, coupled with the expression for operating frequency vs. the permittivity are then used to understand the bias field vs. frequency behavior of the antenna. Finally, the effect of the macroscopic variables on the antenna radiation efficiency is discussed.

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