Cylindrically periodic dielectric waveguide at submillimeter waves

In the terahertz band, the availability of dielectric materials for fabrication of long waveguides is very limited. The only viable candidate at the current time appears to be fused quartz which unfortunately has a relatively low dielectric constant. This limits the use of standard Brag fibers which rely on higher dielectric constants. To overcome this limitation, we have examined the possibility of using a small number of low dielectric constant layers in a periodic arrangement and enclosing the entire structure with a metalic boundary. This configuration results in a moderate loss waveguide. Future work will include the manufacture and testing of such structures and a study of the bend losses

Physical optics characterization of a THz time domain system: UWB leaky lens antenna vs. Austin switch

In this work we show that a THz time domain system based on photoconductive antennas can be improved by over one order of magnitude by using the Ultra-wideband (UWB) leaky lens antenna. The system has been analyzed by implementing a physical optics method to characterize radiated fields by a silicon lens

Fluctuations in the electron system of a superconductor exposed to a photon flux

We report on fluctuations in the electron system, Cooper pairs and quasiparticles, of a superconducting aluminium film. The superconductor is exposed to pair-breaking photons (1.54 THz), which are coupled through an antenna. The change in the complex conductivity of the superconductor upon a change in the quasiparticle number is read out by a microwave resonator. A large range in radiation power can be chosen by carefully filtering the radiation from a blackbody source. We identify two regimes. At high radiation power, fluctuations in the electron system caused by the random arrival rate of the photons are resolved, giving a straightforward measure of the optical efficiency (48%). At low radiation power fluctuations are dominated by excess quasiparticles, the number of which is measured through their recombination lifetime

UWB leaky lens antenna as an improved performance emitter in a THz time domain system

In this contribution we introduce the use of the UWB leaky lens antenna as an improved photo-conducting emitter for a THz time domain system. The UWB antenna presents nearly constant impedance and directive symmetric patterns over a decade of frequency bandwidth. Currently, we are working towards the fabrication of a demonstrating prototype

Problem-matched basis functions for microstrip coupled slot antennas based on Transmission Line Green's Functions (TLGF)

Problem matched basis functions are proposed for the method of moments analysis of printed slot coupled microstrips. The appropriate equivalent currents of the integral equation kernel are represented in terms of two sets of entire domain basis functions. These functions synthesize on one hand the resonant behavior of slots, microstrips or dipoles and on the other hand the field in proximity of the feeding source and of the discontinuities. In order to define these basis functions, canonical geometries are identified, whose Green's functions have been found in semi-analytical form. The accuracy and the effectiveness of the method in terms of convergence rate and number of unknowns is demonstrated by comparison with a standard fine meshing full-wave analysis. The method is extremely convenient for large arrays, where the subwavelength details should be treated together with large global dimensions. Since the proposed solution is independent of the dimensions of these details, it provides dramatic reduction of the number of unknowns and improvement of condition number

EBG enhanced feeds for the improvement of the aperture efficiency of reflector antennas

We describe the use of electromagnetic bandgap (EBG) super-layers to improve the shape of reflectors illumination function. Following an investigation of the leaky wave pole singularities of the EBG Green's function, the shape of the radiation patterns of small apertures in ground planes are optimized. The maximization of the reflector aperture efficiency can be obtained by properly tuning the super layers geometrical parameters. A prototype of such feed has been designed, manufactured and tested. The results indicate that the inclusion of the EBG, increases the aperture efficiency of the feed+reflector system to values higher than 80%, over a 10% bandwidth. These low profile feeds are compatible with printed circuit board and/or integrated technology

Properties of leaky waves supported by grounded dielectric super-layers and implications on the design of reflector feeds

The design strategy that uses dielectric super-layers with neighboring wave-guides closed in matched loads constitutes a worst case scenario as far as the performance enhancement is concerned and finds applicability in radiometric imaging arrays. On the other side the design strategy that uses dielectric super-layers with neighboring wave-guides closed in properly tuned reactive loads can be seen as best case scenario representative of a multi beam system for a telecommunication satellite with independent channels

Characterization of the THz quasi-optical channel for the measurement of the power radiated by photoconductive antennas

In this paper a rigorous electromagnetic characterization of the setup for measuring the THz power radiated by pulsed photoconductive antenna is discussed. Such characterization is expressed in terms of efficiencies which quantify how much power is lost in the coupling between the various components involved in the measurement setup. The conducted analysis highlights how such efficiencies affect the energy spectrum of the measured pulsed signal. Measurement results with two different detectors will be shown during the conference and will be compared against the power estimation obtained by a recently developed equivalent circuit model for photoconductive antennas. The proposed electromagnetic modeling allows us to effectively improve the design of THz time domain systems

Multi-omic profiling of a newly isolated Oxy-PAH degrading specialist from PAH-contaminated soil reveals bacterial mechanisms to mitigate the risk posed by polar transformation products

Polar biotransformation products have been identified as causative agents for the eventual increase in genotoxicity observed after the bioremediation of PAH-contaminated soils.Their further biodegradation has been described under certain biostimulation conditions; however, the underlying microorganisms and mechanisms remain to be elucidated. 9,10-Anthraquinone (ANTQ), a transformation product from anthracene (ANT), is the most commonly detected oxygenated PAH (oxy-PAH) in contaminated soils. Sand-in-liquid microcosms inoculated with creosote-contaminated soil revealed the existence of a specialized ANTQ degrading community, and Sphingobium sp. AntQ-1 was isolated for its ability to grow on this oxy-PAH. Combining the metabolomic, genomic, and transcriptomic analyses of strain AntQ-1, we comprehensively reconstructed the ANTQ biodegradation pathway. Novel mechanisms for polyaromatic compound degradation were revealed, involving the cleavage of the central ring catalyzed by Baeyer−Villiger monooxygenases (BVMO). Abundance of strain AntQ-1 16S rRNA and its BVMO genes in the sandin-liquid microcosms correlated with maximum ANTQ biodegradation rates, supporting the environmental relevance of this mechanism. Our results demonstrate the existence of highly specialized microbial communities in contaminated soils responsible for processing oxy-PAHs accumulated by primary degraders. Also, they underscore the key role that BVMO may play as a detoxification mechanism to mitigate the risk posed by oxy-PAH formation during bioremediation of PAH-contaminated soils