Mr. Jose G. Colom-Ustariz Profile

Jose G. Colom-Ustariz

at Univ of Puerto Rico/Mayaguez

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Proceedings Article | 18 April 2003 Paper

Modeling, simulation, and comparison study of cirrus cloud ice crystals

Jorge Villa, Sandra Cruz-Pol, Jose Colom-Ustariz, Stephen Sekelsky

Proceedings Volume 4882, (2003) https://doi.org/10.1117/12.463034

KEYWORDS: Clouds, Crystals, Crystallography, Atmospheric particles, Particles, Atmospheric modeling, Backscatter, Remote sensing, Atmospheric sensing, Radar

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Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles' size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured by airborne instruments, specifically ice bullets. These can be found depending on the temperature and cloud altitude, isolated or in groups of two or more bullets, called bullet rosettes. The model of the bullets was developed using the parameters obtained by airborne measurements from the National Center for Atmospheric Research (NCAR) Video Ice Particle Sampler (VIPS). This is an airborne instrument that takes samples of the cirrus cloud particles sizes. With these sample parameters we created a bullet function in DDSCAT with the actual shape of the bullets. This software allows us to create irregular models of particles using the Discrete Dipole Approximation method. With this model we can analyze the backscattering produced by the bullet and rosette model or reflectivity and compute the total volume backscattering coefficient from the cirrus clouds. Various models of ice crystal habits are compared.

Proceedings Article | 8 April 2003 Paper

Frequency-agile microwave components using ferroelectric materials

Jose Colom-Ustariz, Rafael Rodriguez-Solis, Salmir Velez, Snaider Rodriguez-Acosta

Proceedings Volume 4881, (2003) https://doi.org/10.1117/12.463043

KEYWORDS: Microwave radiation, Antennas, Multilayers, Dielectrics, Thin films, Ferroelectric materials, Amplifiers, Electronics, Sensors, Phase shifts

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The non-linear electric field dependence of ferroelectric thin films can be used to design frequency and phase agile components. Tunable components have traditionally been developed using mechanically tuned resonant structures, ferrite components, or semiconductor-based voltage controlled electronics, but they are limited by their frequency performance, high cost, hgih losses, and integration into larger systems. In contrast, the ferroelectric-based tunable microwave component can easily be integrated into conventional microstrip circuits and attributes such as small size, light weight, and low-loss make these components attractive for broadband and multi-frequency applications. Components that are essential elements in the design of a microwave sensor can be fabricated with ferroelectric materials to achieve tunability over a broad frequency range. It has been reported that with a thin ferroelectric film placed between the top conductor layer and the dielectric material of a microstrip structure, and the proper DC bias scheme, tunable components above the Ku band can be fabricated. Components such as phase shifters, coupled line filters, and Lange couplers have been reported in the literature using this technique. In this wokr, simulated results from a full wave electromagnetic simulator are obtained to show the tunability of a matching netowrk typically used in the design of microwave amplifiers and antennas. In addition, simulated results of a multilayer Lange coupler, and a patch antenna are also presented. The results show that typical microstrip structures can be easily modified to provide frequency agile capabilities.

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