Publications

Refine Results

(Filters Applied) Clear All

Spatially-resolved individual particle spectroscopy using photothermal modulation of Mie scattering

Summary

We report a photothermal modulation of Mie scattering (PMMS) method that enables concurrent spatial and spectral discrimination of individual micron-sized particles. This approach provides a direct measurement of the "fingerprint" infrared absorption spectrum with the spatial resolution of visible light. Trace quantities (tens of picograms) of material were deposited onto an infrared transparent substrate and simultaneously illuminated by a wavelength-tunable intensity-modulated quantum cascade pump laser and a continuous-wave 532 nm probe laser. Absorption of the pump laser by the particles results in direct modulation of the scatter field of the probe laser. The probe light scattered from the interrogated region is imaged onto a visible camera, enabling simultaneous probing of spatially-separated individual particles. By tuning the wavelength of the pump laser, the IR absorption spectrum is obtained. Using this approach, we measured the infrared absorption spectra of individual 3 um PMMA and silica spheres. Experimental PMMS signal amplitudes agree with modeling using an extended version of the Mie scattering theory for particles on substrates, enabling the prediction of the PMMS signal magnitude based on the material and substrate properties.
READ LESS

Summary

We report a photothermal modulation of Mie scattering (PMMS) method that enables concurrent spatial and spectral discrimination of individual micron-sized particles. This approach provides a direct measurement of the "fingerprint" infrared absorption spectrum with the spatial resolution of visible light. Trace quantities (tens of picograms) of material were deposited onto...

READ MORE

Photothermal speckle modulation for noncontact materials characterization

Summary

We have developed a noncontact, photothermal materials characterization method based on visible-light speckle imaging. This technique is applied to remotely measure the infrared absorption spectra of materials and to discriminate materials based on their thermal conductivities. A wavelength-tunable (7.5-8.7 um), intensity-modulated, quantum cascade pump laser and a continuous-wave 532 nm probe laser illuminate a sample surface such that the two laser spots overlap. Surface absorption of the intensity-modulated pump laser induces a time-varying thermoelastic surface deformation, resulting in a time-varying 532 nm scattering speckle field from the surface. The speckle modulation amplitude, derived from a series of visible camera images, is found to correlate with the amplitude of the surface motion. By tuning the pump laser's wavelength over a molecular absorption feature, the amplitude spectrum of the speckle modulation is found to correlate to the IR absorption spectrum. As an example, we demonstrate this technique for spectroscopic identification of thin polymeric films. Furthermore, by adjusting the rate of modulation of the pump beam and measuring the associated modulation transfer to the visible speckle pattern, information about the thermal time constants of surface and sub-surface features can be revealed. Using this approach, we demonstrate the ability to distinguish between different materials (including metals, semiconductors, and insulators) based on differences in their thermal conductivities.
READ LESS

Summary

We have developed a noncontact, photothermal materials characterization method based on visible-light speckle imaging. This technique is applied to remotely measure the infrared absorption spectra of materials and to discriminate materials based on their thermal conductivities. A wavelength-tunable (7.5-8.7 um), intensity-modulated, quantum cascade pump laser and a continuous-wave 532 nm...

READ MORE

Multi-lithic phased array architecture for airborne sense and avoid radar

Published in:
2013 IEEE Int. Symp. On Phased Array Systems and Technology, 15-18 October 2013.

Summary

Transmit and receive Ku-band phased array designs are described for testing an airborne sense and avoid radar. The arrays are small with a size of 24 cm x 9 cm and operate from 13 to 17 GHz with electronic scanning from plus of minus 45 degrees in azimuth and plus of minus 30 degrees in elevation. A novel design architecture allows the use of multiple multilayered printed circuit boards and simple air cooling.
READ LESS

Summary

Transmit and receive Ku-band phased array designs are described for testing an airborne sense and avoid radar. The arrays are small with a size of 24 cm x 9 cm and operate from 13 to 17 GHz with electronic scanning from plus of minus 45 degrees in azimuth and plus...

READ MORE

Stepped notch antenna array used as a low thermal resistance heat sink

Published in:
IEEE Antennas and Propagation Society Int. Symp. 2013, 7-13 July 2013.

Summary

A stepped notch antenna at Ku-band is developed to provide a thermal heat sink for active arrays. The antenna with forced air cooling provides up to 0.4 degrees C/W of thermal resistance. The antenna integration with a printed circuit board allows for high volume surface mount assembly of active devices.
READ LESS

Summary

A stepped notch antenna at Ku-band is developed to provide a thermal heat sink for active arrays. The antenna with forced air cooling provides up to 0.4 degrees C/W of thermal resistance. The antenna integration with a printed circuit board allows for high volume surface mount assembly of active devices.

READ MORE

Nanosatellites for Earth environmental monitoring: the MicroMAS project

Summary

The Micro-sized Microwave Atmospheric Satellite (MicroMAS) is a 3U cubesat (34x10x10 cm, 4.5 kg) hosting a passive microwave spectrometer operating near the 118.75-GHz oxygen absorption line. The focus of the first MicroMAS mission (hereafter, MicroMAS-1) is to observe convective thunderstorms, tropical cyclones, and hurricanes from a near-equatorial orbit at approximately 500-km altitude. A MicroMAS flight unit is currently being developed in anticipation of a 2014 launch. A parabolic reflector is mechanically rotated as the spacecraft orbits the earth, thus directing a cross-track scanned beam with FWHM beamwidth of 2.4-degrees, yielding an approximately 20-km diameter footprint at nadir incidence from a nominal altitude of 500 km. Radiometric calibration is carried out using observations of cold space, the earth?s limb, and an internal noise diode that is weakly coupled through the RF front-end electronics. A key technology feature is the development of an ultra-compact intermediate frequency processor module for channelization, detection, and A-to-D conversion. The antenna system and RF front-end electronics are highly integrated and miniaturized. A MicroMAS-2 mission is currently being planned using a multiband spectrometer operating near 118 and 183 GHz in a sunsynchronous orbit of approximately 800-km altitude. A HyMAS- 1 (Hyperspectral Microwave Atmospheric Satellite) mission with approximately 50 channels near 118 and 183 GHz is also being planned. In this paper, the mission concept of operations will be discussed, the radiometer payload will be described, and the spacecraft subsystems (avionics, power, communications, attitude determination and control, and mechanical structures) will be summarized.
READ LESS

Summary

The Micro-sized Microwave Atmospheric Satellite (MicroMAS) is a 3U cubesat (34x10x10 cm, 4.5 kg) hosting a passive microwave spectrometer operating near the 118.75-GHz oxygen absorption line. The focus of the first MicroMAS mission (hereafter, MicroMAS-1) is to observe convective thunderstorms, tropical cyclones, and hurricanes from a near-equatorial orbit at approximately...

READ MORE

Microgrid study: energy security for DoD installations

Summary

Growing concerns about the vulnerability of the electric grid, uncertainty about the cost of oil, and an increase in the deployment of renewable generation on domestic military installations have all led the Department of Defense (DoD) to reconsider its strategy for providing energy security for critical domestic operations. Existing solutions typically use dedicated backup generators to service each critical load. For large installations, this can result in over 50 small generators, each servicing a low voltage feeder to an individual building. The system as a whole is typically not well integrated either internally, with nearby renewable assets, or to the larger external grid. As a result, system performance is not optimized for efficient, reactive, and sustainable operations across the installation in the event of a power outage or in response to periods of high stress on the grid. Recent advances in energy management systems and power electronics provide an opportunity to interconnect multiple sources and loads into an integrated system that can then be optimized for reliability, efficiency, and/or cost. These integrated energy systems, or microgrids, are the focus of this study. The study was performed with the goals of (1) achieving a better understanding of the current microgrid efforts across DoD installations, specifically those that were in place or underway by the end of FY11, (2) categorizing the efforts with a consistent typology based on common, measurable parameters, and (3) performing cost-benefit trades for different microgrid architectures. This report summarizes the results of several months of analysis and provides insight into opportunities for increased energy security, efficiency, and the incorporation of renewable and distributed energy resources into microgrids, as well as the factors that might facilitate or impede implementation.
READ LESS

Summary

Growing concerns about the vulnerability of the electric grid, uncertainty about the cost of oil, and an increase in the deployment of renewable generation on domestic military installations have all led the Department of Defense (DoD) to reconsider its strategy for providing energy security for critical domestic operations. Existing solutions...

READ MORE

Showing Results

1-6 of 6