Quasi-optical antenna-mixer-array design for terahertz frequencies

A new quasi-optical antenna-mixer-array design for terahertz frequencies is presented. In the design, antenna and mixer are combined into an entity, based on the technology in which millimeter-wave horn antenna arrays have been fabricated in silicon wafers. It consists of a set of forward- and backward-looking horns made with a set of silicon wafers. The front side is used to receive incoming signal, and the back side is used to feed local oscillator signal. Intermediate frequency is led out from the side of the array. Signal received by the horn array is picked up by antenna probes suspended on thin silicon-oxynitride membranes inside the horns. Mixer diodes will be located on the membranes inside the horns. Modeling of such an antenna-mixer-array design is done on a scaled model at microwave frequencies. The impedance matching, RF and LO isolation, and patterns of the array have been tested and analyzed

Probe modeling for millimeter-wave integrated-circuit horn antennas

Integrated-circuit probe-excited horn-antenna arrays etched in silicon are well developed. They are a very promising class of antenna arrays for milli-meter and submillimeter applications. Further development of this technology involves integrating mixers and amplifiers into the antenna arrays. In an effort to develop an antenna-mixer array based on the existing technology, various antenna probes inside the pyramidal horns have been examined on scaled model-horns at the microwave frequencies. In this paper, modeling results and design principles of these antenna probes have been presented, which include the resonant impedance, the operating frequency, and the bandwidth of the horn antennas. These measurement results provide a guideline in designing probes for millimeter/submillimeter-wave integrated-circuit horn-antenna-mixer arrays

Aperture efficiency of chemically etched horns at 93 GHz

The aperture efficiency of monolithic two-dimensional horn imaging arrays has been optimized at 93 GHz. The imaging arrays consist of several silicon wafers into which arrays of pyramidal horns are etched chemically. Dipole antennas and detectors are suspended on thin silicon oxynitride membranes on one of the central silicon wafers about halfway down the horns. The devices are 7×7 arrays with a 1 λ opening and a 71° flare angle. Antenna impedances have been measured on a low-frequency model. A variety of millimeter-wave dipole antennas and bolometers have been designed and tested. A large-area bismuth thin-film power meter is used to obtain accurate absolute power. The measured aperture efficiency improved from 44% to 72%. The highest system coupling efficiency with a lens was 36% including lens absorption and reflection losses

Risk Analysis of Organic Cropping Systems in Minnesota

When all strategies received conventional market prices, 4-year cropping sequences had greater net returns than 2-year sequences, and the organic input, 4-year strategy had the highest net return. Adding 50% of the estimated organic premium, the 4-year, organic strategy dominated all low- and high-purchased input strategies.Crop Production/Industries, Risk and Uncertainty,

A theoretical study of the conversion of gas phase methanediol to formaldehyde

Methanediol, or methylene glycol, is a product of the liquid phase reaction of water and formaldehyde and is a predicted interstellar grain surface species. Detection of this molecule in a hot core environment would advance the understanding of complex organic chemistry in the interstellar medium, but its laboratory spectroscopic characterization is a prerequisite for such observational searches. This theoretical study investigates the unimolecular decomposition of methanediol, specifically the thermodynamic and kinetic stability of the molecule under typical laboratory and interstellar conditions. Methanediol was found to be thermodynamically stable at temperatures of <100 K, which is the characteristic temperature range for interstellar grain mantles. The infinite-pressure RRKM unimolecular decomposition rate was found to be <10^(−18) s^(−1) at 300 K, indicating gas phase kinetic stability for typical laboratory and hot core temperatures. Therefore, both laboratory studies of and observational searches for this molecule should be feasible

Quantum-mechanical calculations of the stabilities of fluxional isomers of C_4H_7^+ in solution

Although numerous quantum calculations have been made over the years of the stabilities of the fluxional isomers of C4H7+, none have been reported for other than the gas phase (which is unrealistic for these ionic species) that exhibit exceptional fluxional properties in solution. To be sure, quantum-mechanical calculations for solutions are subject to substantial uncertainties, but nonetheless it is important to see whether the trends seen for the gas-phase C4H7+ species are also found in calculations for polar solutions. Of the C4H7+ species, commonly designated bisected-cyclopropylcarbinyl 1, unsym-bicyclobutonium-2, sym-bicyclobutonium 3, allylcarbinyl 4, and pyramidal structure 6, the most advanced gas-phase calculations available thus far suggest that the order of stability is 1 ≥ 2 ≥ 3 >> 4 >> 6 with barriers of only ~1 kcal/mol for interconversions among 1, 2, and 3. We report here that, when account is taken of solvation, 2 turns out to be slightly more stable than 1 or 3 in polar solvents. The pattern of the overall results is unexpected, in that despite substantial differences in structures and charge distributions between the primary players in the C4H7+ equilibria and the large differences in solvation energies calculated for the solvents considered, the differential solvent effects from species to species are rather small

Influence of non-dipole field on determination of Plio-Pleistocene true polar wander

Some studies of global paleomagnetic data have found an offset of the magnetic pole during the Plio-Pleistocene which has been interpreted as indicating a period of rapid True Polar Wander, with a rate of movement comparable to the present-day rate of polar motion deduced from astronomical observations. We show that much of the polar offset determined from the paleomagnetic data may be due to deviations in pole position caused by persistent non-dipole zonal components of the geomagnetic field. A correction of paleomagnetic poles for the long-term non-dipole field reduces the polar offset and thus suggests a slower or shorter episode of True Polar Wander over the past 5 million years

Inclination anomalies from Indian Ocean sediments and the possibility of a standing non-dipole field

We report magnetic inclinations measured in deep-sea sediments of the equatorial Indian Ocean which record the behavior of a nondipole component of the timeaveraged geomagnetic field during the Plio-Pleistocene (0-5 Ma). The magnitude of the nondipole effect recorded in these sediments appears to depend on polarity state, with inclinations showing departures from geocentric axial dipole directions which are small (2°) during normal polarity and larger (5°) during reverse polarity times. The overall nondipole effect observed here is consistent with prior spherical harmonic estimates of the paleomagnetic field; the polarity bias found agrees, in both sense and magnitude, with earlier reports of polarity asymmetry in the low-degree zonal harmonic fields. The presence of this asymmetry supports previous suggestions of the existence of a standing component of the nondipole field which does not invert during reversals of the main field. We explore whether the standing field so indicated may have influenced paleomagnetic directions recorded during polarity transitions at other equatorial sites

Mechanical Properties of Red Maple Structural Lumber

Efficient utilization of hardwood structural lumber depends on developing better procedures of grading and property assignment. In this study, we evaluated the properties of red maple 2- by 4-in. (standard 38- by 89-mm) lumber tested in bending and in tension and compression parallel to the grain and compared the results to published values derived by ASTM D 245 clear wood procedures. The results indicate that significant increases in allowable properties could be obtained using procedures based on tests of full-size lumber. The results also demonstrate that the relationships between lumber strength in compression parallel to grain and bending strength and between tension parallel to grain and bending strength are similar to those for softwood species. Thus, procedures used to assign properties to mechanically graded softwood species should be applicable to red maple