UHF Energy Research Articles

UHF Energy Harvesting based on a reflector-backed bowtie antenna

UHF Energy Harvesting based on a reflector-backed bowtie antenna

UHF energy application in acceleration technology and radiolocation

The article discusses the solution to the problem of increasing the output power and efficiency of devices using high-current relativistic electron flows.

Drying Kinetics of Sunflower Seeds using Pulsed UHF Energy Intake

In this paper the drying kinetics of sunflower seeds using pulsed UHF energy intake are given. It is shown and argued that the application of pulsed internal heat source made possible the reduction of heat treatment period by 17%, and of specific energy consumption by 21.8%.

Three, four and five interacting electrons in a spherical box: an exact diagonalization studyextended

We study the problem of N electrons confined to a hard three-dimensional spherical box, forN = 3,4 and 5. Full-configuration interaction and Hartree–Fock calculations have been performed. Wereport energies, densities, second-order density matrices and exchange–correlation holes. In theN = 4 system, we observe a spin transition as the radiusR of the sphere is increased, changing the ground state from3P to5S. TheN = 3 and 5 systemsremain 2P and4S, respectively,for all R investigated. Pair-correlation functions and physical exchange–correlation holes have beencomputed over a regime in which the systems transform from liquid droplets to Wigner molecules.These functions show marked, yet characteristic, changes in this regime. By computing|Ec/E|,where Ec is the correlation energy defined with respect to the unrestricted Hartree–Fock solution, weshow that the maximum relative error in the UHF energies occurs in this crossover regime.These systems provide challenging benchmarks for post-Hartree–Fock and densityfunctional theory methods.

Hybrid Hartee–Fock/density functional (HF/DF) calculations of adiabatic electron affinities (EA ad's) of neutral hydroquinone radicals of 1,4-benzoquinone ( 1) and 1,4-benzoquinone imine ( 2)

The adiabatic electron affinities (EA ad's) of the neutral hydroquinone radicals of 1 and 2, i.e., 1 · and 2 · , have been investigated by several quantum chemical models. The B3LYP and B3PW91 methods, used with the 6-311G( d, p) basis set, underestimated the EA ad's by about 6–8 kcal/mol, but with the 6-31+G( d) and 6-311+G( d, p) basis sets, results that are in reasonable accord with experiment were obtained, indicating the importance of diffuse functions for anions in the hybrid HF/DF calculations of EA ad's. The B3LYP-calculated results, including those for 1 and 2 (Y.H. Mariam, L. Chantranupong, J. Comput.-Aided Mol. Design 11 (1997) 345), along with literature values for the EA ad's of the phenyl and phenylnitrene radicals, give the trend in EA ad's that follows the order: phenoxyl (50.6)> 1 · (44.7)> 1 (43.7)> 2 · (38.7)>anilino (36.5)> 2 (34.7)>phenylnitrene (33.4)>phenyl (27.7). Apparently, the EA ad's of both radicals 1 · and 2 · are, respectively, greater than the EA ad's of the parent quinone and iminoquinone 1 and 2. UHF, PUHF, UMP2 and PMP2 energy calculations using B3LYP/6-311+G geometries gave wavefunctions that were found to be highly spin contaminated, and the UHF, PUHF and PMP2 models underestimated the EA ad's, while the UMP2 and the AM1 half-electron results were overestimated. Spin annihilation (in the UHF and UMP2 formalisms) of the first contaminant (quartet) does not apparently remove all the spin contamination. The results indicate, in addition to gradient corrections to the Slater exchange and the correlation functionals (Y.H. Mariam, L. Chantranupong, J. Comput.-Aided Mol. Design 11 (1997) 345), correlation, spin annihilation and inclusion of diffuse functions are important in B3LYP calculations of electron affinities for the systems studied in this work. Since the 6-31+G( d) basis set, with considerably less basis functions, is computationally less costly than the 6-311+G( d, p) basis set, it is recommended for quinone systems of interest where the computational cost is a consideration. The transferability of this computational model to larger systems is not, however, warranted and further work is needed.

FD-TD modeling of digital signal propagation in 3-D circuits with passive and active loads

Most existing computer-aided circuit design tools are limited when digital clock speeds exceed several hundred MHz. These tools may not deal effectively with the physics of UHF and microwave electromagnetic wave energy transport along metal surfaces such as ground planes or in the air away from metal paths that are common at or above this frequency range. In this paper, we discuss full-wave modeling of electronic circuits in three dimensions using the finite-difference time-domain (FD-TD) solution of Maxwell's equations. Parameters such as stripline complex line impedance, propagation constant, capacitance per unit length and inductance per unit length can be easily computed as a function of frequency. We also discuss FD-TD Maxwell's equations computational modeling of lumped-circuit loads and sources in 3-D, including resistors and resistive voltage sources, capacitors, inductors, diodes, and transistors. We believe that this approach will be useful in simulating the large-signal behavior of very high-speed nonlinear analog and digital devices in the context of the full-wave time-dependent electromagnetic field. >

On incorrect behavior of single annihilation equations of spin-projected UHF and UMP energies

Approximate (i.e. single annihilation) equations for the spin-projected UHF and UMP energies as well as the 〈 Ŝ〉 expectation value for the spin state S give incorrect results under the single projection, i.e. when only the next higher-spin ( S + 1) contaminant is projected out. This originates from the fact that every time the annihilator operates, the wavefunctions of higher-spin contaminants change sign. On the other hand, single annihilation equations with double projection of both S + 1 and S + 2 spin contaminants show correct behavior and recommended for practical applications.

Investigation of mode coupling in a multimode superconducting cavity to store and extract UHF energy

Investigation of mode coupling in a multimode superconducting cavity to store and extract UHF energy

Ab initio SCF and CI study of the cyclopropane/trimethylene radical cations

The ab initio UHF energy surface for the ring opening process leading from the cyclopropane cation to the trimethylene radical cation has been calculated. The trimethylene radical cation is found to correspond to a saddle point on the energy hypersurface, having C s geometry with one of the methylene groups twisted 90° and a π electronic state. Further optimization of this species at the MP2/6-31G* level converges to a geometry of C 2v symmetry. Hyperfine coupling constants for the cyclopropane and trimethylene radical cations at their UHF and MP2/6-31G* optimized geometries have been calculated using accurate CI wavefunctions, and the calculated data are discussed together with published ESR data. For the cyclopropane cation, no evidence for a ground state of symmetry lower than C 2v has been found.

The Effect of Ultrahighfrequency Electromagnetic Energy on Adenosine Triphosphatase Activity in Germinating Weed Seeds1

Abstract UHF Electromagnetic energy (2450 MHz) is lethal at dosages from 100-200 J/cm2 to seeds of several weed species. Seeds were exposed to uniform energies by placing them in a quartz tube and inserting the tube in a waveguide. Seeds of barnyard grass, (Echinochlea crusgalli (L.) Beauv.), large crabgrass (Digitaria sauginalis (L.) and common purslane (Portulaca oleracea L.) showed no visible external damage when viewed in the scanning electron microscope at up to 5,000 × after treatment. No discernible internal damage was visible when tissues were immediately fixed and viewed by transmission electron microscopy after receiving minimum lethal dosages of UHF energy. At higher UHF dosages, membrane breakage and loss of integrity of organelles was observed. ATPase activity in treated seeds was monitored by transmission electron microscopy as an indicator of possible UHF destruction of enzymes. ATPase activity of tissues was absent after minimal or higher dosages of microwaves. Cells receiving minimal UHF treatment otherwise appeared normal. Toxicity from microwaves may occur as a result of selective heating of cells which results in partial protein denaturization and inactivation of key enzymes.

Some Factors Which Influence the Toxicity of UHF Energy to Weed Seeds

UHF energy (2450 MHz) was applied to seeds and seed-soil mixtures with a waveguide under controlled conditions. After treatment, seeds were germinated at 27 C to determine viability. Seeds were either killed or seedlings grew normally with no intermediate levels of inhibition typical of that produced with sub-lethal dosages of herbicides. The energy required to kill several species of dry seeds ranged from 88 to 183 J/cm2and could be reduced 12 to 42% by a 24-hr imbibition period prior to treatment. When several seed-soil mixtures were treated, the greatest toxicity occurred in a moist muck and clay loam soil, with the least toxicity on a dry loamy sand soil. Although attenuation of activity occurred in dry soils of three types, less energy was required to kill seeds in moist soils than was required in the absence of soil. Increasing the power levels reduced the time of exposure necessary to kill barnyardgrass [Echinochloa crus-galli(L.) Beauv.] seeds. Less energy was required to kill seeds as the soil temperature was increased from −20 to +18 C.

Uhf Electromagnetic Energy for Weed Control in Vegetables

UHF energies (45 to 730 j/cm2, 2450 MHz) were applied to irrigated and non-irrigated soils in the field just before planting of cantaloupe (Cucumis meloL., var.reticulatusNaudin) and onion (Allium cepaL.) to study the influence of UHF energy on plant growth. London rocket (Sisymbrium irioL.) and sunflower (Helianthus annuusL.) were controlled with 180 j/cm2of UHF energy applied after seed had imbibed water from soil. These species and ridgeseed spurge (Euphorbia glyptospermaEngelm.), redroot pigweed (Amaranthus retroflexusL.), common purslane (Portulaca oleraceaL.), and Japanese millet [Echinochloa frumentacea(Roxb.) Link.] were controlled with 360 j/cm2(0.0048 kmph) regardless of seed or soil moisture. London rocket and sunflower were not controlled by several soil-incorporated herbicides. UHF energy had no deleterious effects on the growth of cantaloupe or onion and tended to increase the yields above those of the hand-weeded vegetables. Phytotoxic UHF radiation penetrated 7.5 and 10 cm in irrigated and non-irrigated soil, respectively, at 360 j/cm2. Soil temperature after UHF treatment increased with increasing UHF energy levels and decreasing soil moisture and depth.

Pi electron states of the cyclopentadienyl cation: A comparison of complete CI and UHF results

Complete CI pi electron wavefunctions and energy levels are calculated for the cyclopentadienyl cation and compared to the UHF results of Phillips and Schug [J. Chem. Phys. 57, 3498 (1972)]. The projected UHF and CI energies for the lowest singlet (1E2′) and triplet (3A2′) states are in good agreement, but energies of the projected excited states do not correspond to the lowest CI levels of the same symmetry. In the UHF 1E2′ and 3A2′ wavefunctions, the contribution of excited configurations is smaller than in the CI functions.

A perturbation treatment of the hartree-fock equations for the ground states of 3- to 10-electron atoms

The first-order hartree-fock (hf) equations for the ground state of atomic systems with 4 to 10 electrons are deduced from the corresponding unrestricted (uhf) equations given previously. The second-order hf energies are given exactly and the third-order energies very accurately. Each atom is treated as a special case of a general scheme. The third- order energy of lithium is calculated very accurately, completing linderberg's calculation. The hf ground state energies of atoms with 3-10 electrons are shown to differ very little from the corresponding uhf energies previously given. The zero- and first-order expectation values of various operators are related to their corresponding uhf values.

A perturbation treatment of the unrestricted hartree-fock equations for the ground states of 3- to 10-electron atoms

The first order unrestricted hartree-fock equations for the ground states of atomic systems with 4,5,...,10 electrons are solved exactly. The solutions are used to evaluate the corresponding second order energies exactly and the third order energies very accurately. A method is described whereby each atom can be treated as a special case of a general scheme. The third order uhf energy of lithium has been recalculated with greater accuracy and comparison is made between the uhf energy values obtained for the ground states of all the second row atoms and those obtained by other methods. The zero-order and first-order terms in the expectation values of the operators l?2and s?2are calculated and tables are given leading to those of 1/r3, 1/r, r, r2and delta(r).

Investigations on the Unrestricted Hartree–Fock Method as a Tool for Computing Potential Surfaces

The possible uses of the ab initio spin-unrestricted Hartree–Fock (UHF) method for computing potential energy surfaces have been investigated, expanding the molecular orbitals from a basis set of Gaussian functions. In order to approximate spin-pure states, an exact spin projection operator, as well as an operator annihilating only the state of next higher multiplicity, has been used. Preliminary studies undertaken on the H2 and LiH molecules indicate that among the various methods employed, the unprojected UHF approach gives the most satisfactory shape for potential curves. The HNO molecule was then investigated, and five electronic states of the system were considered, namely A1,A″3,A″1 symmetry. The ground state is A′1. Its UHF energy was minimized by varying the three geometrical parameters independently. A value of 〈Ŝ2〉 of 0.32 was obtained at the experimental geometry. This system with an even number of electrons thus has the unexpected property of being unstable with respect to a splitting of the α and β orbitals. Application of the spin projection operator lowers the energy by 0.0265 a.u. The UHF wavefunctions give an excitation energy A″1←A′1 of 3860 cm−1. When pure spin states are produced, it becomes 11 660 cm−1 (experimental value 13 150 cm−1). The A″3 state practically coincides with the ground state in the UHF approximation, but after projection an excitation energy of 5850 cm−1 is obtained. A slight maximum is observed in the UHF potential energy curve of the A″ states as a function of the N–H distance, which we associate with the predissociation observed in the spectrum of the compound. Based upon projection at the experimental minimum for the ground state, and at infinite N–H separation, a set of adjusted curves has been generated for the system H + NO. The features of these curves are discussed in relation with the mechanism of the recombination reaction between hydrogen atoms and nitric oxide.

Modeling UHF transhorizon scatter propagation

A laboratory model of a transhorizon propagation path has been used in an experiment designed to simulate the transmission of UHF energy beyond the radio horizon via the mechanism of tropospheric scatter. Electromagnetic energy was scattered over the radio horizon by dropping very small glass spheres through the beam of the transmitting antenna.

Pulse modulated UHF energy illumination of the heart associated with change in heart rate

Pulse modulated UHF energy illumination of the heart associated with change in heart rate

A coaxial pathway for recording from the cat brain stem during illumination with UHF energy

A coaxial pathway from the cat brain stem to amplifier was developed for recording evoked potentials in an electrically noisy environment, i.e. illumination of an animal with pulse modulated UHF energy. This pathway minimizes the possibility of the energy inducing currents in the recording system and thereby stimulating the brain or driving the amplifier.

Brain stem evoked responses associated with low-intensity pulsed UHF energy.

Brain stem evoked responses associated with low-intensity pulsed UHF energy.