Increasing Excitation Frequency Research Articles

Influence of the applied field frequency on the characteristics of Ar and diffusion plasmas sustained at electron cyclotron resonance above multipolar magnetic field structures

In argon plasmas excited at electron cyclotron resonance above multipolar magnetic field structures, ion density increases linearly with microwave input power but saturates as it gets near the critical density. This behaviour is observed at the three microwave frequencies investigated, namely 960 MHz, 2.45 GHz, and 5.85 GHz, as well as for different magnetic field configurations. The saturation density is independent of the atomic or molecular nature of the gas, as shown with Ar and . Expectedly, the ion density saturation value varies as the square of the excitation frequency, while the microwave input power required to reach saturation is proportional to the critical density. For a given multipolar magnetic field confinement, the electron temperature is shown to decrease with increasing excitation frequency. This result stems from the confinement of the fast electrons, which generate the plasma. The evolution of the F-atom concentration in discharges, as measured by actinometry, is observed to saturate with microwave input power at values depending on gas pressures at both the 2.45 GHz and 5.85 GHz excitation frequencies. Ion density and F-atom concentration saturate at distinct microwave input powers.

Influence of the electric field frequency on the performance of a RF excited CO2 waveguide laser

An analysis is presented of the effect of the RF frequency on the active media of CO2 waveguide lasers. It is found that the characteristics are improved with increasing RF frequency because the space charge sheath width decreases with increasing excitation frequency. We also found that the sheath width decreases with the discharge current; this fact was never discussed before. The higher the exciting frequency the higher is the maximum input power of the discharge in the stable low current mode. It is attractive to extend the input power while keeping the discharge in this mode. Finally, a stabilizing excitation technique is described for the inherent unstable region of the discharge.

Micro swimming mechanisms propelled by external magnetic fields

A new type of micro swimming mechanism is proposed for microrobots working in water. It is composed of a small magnet attached to a spiral wire. An external alternating magnetic field causes the magnet to rotate due to magnetic torque. As a result, the mechanism can swim propelled by waves traveling along the spiral. The swimming velocity increases linearly with increasing excitation frequency, and the increasing rate depends on the shape of the spiral. The experimental velocity agrees with the calculation result based upon Lighthill's theory (1975, 1976).

Experimental and Numerical Study of the Time-Dependent Pressure Response of a Shock Wave Oscillating in a Nozzle

Investigations of flutter in transonic turbine cascades have shown that the movement of unsteady normal shocks has an important effect on the excitation of blades. In order to predict this phenomenon correctly, detailed studies concerning the response of unsteady blade pressures versus different parameters of an oscillating shock wave should be performed, if possible isolated from other flow effects in cascades. In the present investigation the correlation between an oscillating normal shock wave and the response of wall-mounted time-dependent pressure transducers was studied experimentally in a nozzle with fluctuating back pressure. Excitation frequencies between 0 Hz and 180 Hz were investigated. For the measurements, various measuring techniques were employed. The determination of the unsteady shock position was made by a line scan camera using the Schlieren flow visualization technique. This allowed the simultaneous use of unsteady pressure transducers to evaluate the behavior of the pressure under the moving shock. A numerical code, based on the fully unsteady Euler equations in conservative form, was developed to simulate the behavior of the shock and the pressures. The main results of this work were: (1) The boundary layer over an unsteady pressure transducer has a quasi-steady behavior with respect to the phase lag. The pressure amplitude depends on the frequency of the back pressure. (2) For the geometry investigated the shock amplitude decreased with increasing excitation frequency. (3) The pressure transducer sensed the arriving shock before the shock had reached the position of the pressure transducer. (4) The computed unsteady phenomena agree well with the results of the measurements.

Improvement of grain size and deposition rate of microcrystalline silicon by use of very high frequency glow discharge

The influence of the plasma excitation frequency on the growth conditions and the material properties of microcrystalline silicon prepared by plasma enhanced chemical vapor deposition at low deposition temperature is investigated. It is found that an increase of the plasma excitation frequency leads to a simultaneous increase of the growth rate, the grain size, and the Hall mobility of microcrystalline silicon. This is attributed to an effective selective etching of disordered material creating more space to develop crystalline grains, while also more species for faster growth of the crystallites are available.

Pinhole device: a new type of thin film transformer

A novel type of thin film transformer was fabricated using a strip line, an amorphous CoNbZr film, and a ground plane. This thin film transformer has three small pinholes in the magnetic film. The strip line was terminated to the ground plane through the hole. This is called a pinhole device. The output voltage increased with increasing excitation frequency. Applying a DC magnetic field decreased the output voltage above 800 MHz, and increased it below 800 MHz. It is concluded that the pinhole device can be used as a controllable transformer at very high frequencies. >

Preliminary results of vibrator-aided experiments in non-linear seismology conducted at Uetze, F.R.G.

Following acoustics and largely thanks to the pioneering work of a group of Soviet geophysicists, the study of non-linear elastic properties and their effects is becoming an active field of research in geophysics. The research so far has produced a substantial body of evidence indicating that earth materials, from soils to crystalline rocks, are much more non-linear than is commonly believed and certainly far more non-linear than the materials usually used and studied in acoustics. But although most of the evidence comes from vibrator-aided experiments, apparently best suited for investigating the non-linearity of the geophysical medium owing to the ability of modern vibrators to generate seismic signals of prescribed form, the absence of a standard experimental technique makes it difficult to estimate and compare the various results, particularly in view of the considerable non-linearity of the source (vibrator-ground system) itself. The aim of the present vibrator-aided experiments was to try to confirm certain results in non-linear seismology, particularly the effects of harmonic generation and non-linear interaction in vibrator-induced sinusoidal seismic waves, by using an experimental method designed to enable one to discriminate between source, near-field and far-field non-linear effects. In the experiments, two identical prospecting vibrators, installed on the ground surface some 16 m apart, were driven in the harmonic regime separately and simultaneously (tests on non-linear evolution and interaction), a wide range of excitation frequencies and amplitudes being covered, and the resulting ground-surface motion was picked up by an array consisting of 48 groups of 12 vertical geophones-velocimeters and recorded, in multiplex form, by a prospecting seismic station. Tests were made first for short and intermediate source-receiver distances (near field, distance range covered 0–200 m, 5-m spacing of geophone groups), then for large distances (far field, range 1.5–3.5 km, 50-m spacing). A preliminary examination of the field data, available at present for analysis in the form of traces or Fourier spectra, both without amplitude information, indicates the effects of harmonic generation (both in the near and far fields) and non-linear interference (only in the near field) as well as the phenomenon of modulational instability (only in the near field and for very low excitation levels). It seems that, whereas the near field was dominated by surface Rayleigh waves, the far field was dominated by body waves propagated through the water-saturated layer. Lastly, as expected, the baseplate-accelerometer signal, recorded for one of the vibrators, typically contains a large amount of harmonic distortion, usually decreasing with increasing excitation frequency, but somewhat startingly, sometimes decreasing with increasing excitation level.

Threshold photoionization spectra of excited solute electronic states in nonpolar liquids

Photoconductivity spectra are reported for the first excited singlet (S{sub 1}) and triplet (T{sub 1}) states of N,N,N{prime},N{prime}-tetramethyl-p-phenylenediamine (TMPD) in nonpolar organic solvents at room temperature. The measured ionization potentials, corrected for the excited-state energies, agree well with those derived from previously published TMPD ground-state (S{sub 0}) photoionization studies. The excited-state spectra and the S{sub 0} spectrum both increase in magnitude with increasing excitation frequency, first exponentially and then as a power law in excess energy above the ionization threshold. This behavior is similar to that of the absorption spectra of amorphous semiconductors. In each case, direct excitation of the photodonor into the conduction band of the solvent is indicated (instead of autoionization from a superexcited state of TMPD). In one instance unambiguous evidence for this path is encountered.

Magnetostrictive torque sensor performance-nonlinear analysis

The effects on performance of magnetostrictive torque sensors due to nonlinear properties of magnetic materials are analyzed. A solution for the nonlinear problem is described. For constant magnetomotive force (constant current) excitation, nonlinear effects dramatically reduce the predicted output signal of the sensor from that computed using linear models. Saturation and the subsequent fall-off of a sensor signal as excitation current is increased are predicted and agree well with experimental results. The sensor signal continually increases with the increase of excitation frequency. As is shown, this gain must be balanced against growing problems of sensor signal-to-noise ratio, surface-localized noise, and requirements for higher-power/higher-voltage excitation sources.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamic response of a ring fabricated from a non-linear elastic material

The study is concerned with the dynamic in-plane response of circular thin rings, fabricated from a non-linear elastic material. The governing displacement equations of motion are established and solved on the basis of the Galerkin procedure and the method of multiple scales. The results of the analysis of steady state forced vibration indicate that non-linear coupling induces motion not only of the excited mode, but also very strong response of certain other modes. In the case of a slowly increasing excitation frequency, a response similar to the beat phenomenon may develop under certain conditions.

Viscoelastic properties of short fiber filled SBR composites

AbstractThis paper examines the effects of deformation amplitude, temperature and frequency on the dynamic properties of SBR‐short fiber composites. The presence of the fiber increases the storage modulus at any deformation amplitude. Depending on the nature of the fiber, the linear response zone of the modulus versus deformation either diminishes or disappears. The loss factor tan δ is higher in fiber composites. Although the peaks do not vary in magnitude, they occur at different deformation amplitudes.Temperature increase causes the moduli to decrease, the gradient, however, being less pronounced for fiber composites. The relaxation spectra show a damping peak which correlates to the principal relaxation process in the elastomeric matrix. The temperature at which this peak appears is displaced towards higher values with increasing excitation frequency. This allows the determination of the apparent relaxation activation energy, which is higher in fiber plus adhesive composites (225 – 275 kJ/mol), as compared to the fiber‐free composite (194 kJ/mol), as a consequence of stronger fiber‐matrix interaction.

The multi-mode response between deflectional and torsional modes in a beam.

Deflectional and torsional modes of a beam may be coupled by nonlinear terms for large amplitudes. As a problem of deflectional-torsional vibrations coupled by nonlinear terms, the dynamic response of a beam with a thin rectangular cross section subjected to harmonic excitation in the lateral direction is taken up. The possibility of a multi-mode response between deflectional and torsional modes is discussed theoretically. For this, first a general analysis is given. Then, a typical case is taken up in which the natural frequency of the second deflectional mode coincides with that of the first torsional one, and a numerical calculation is conducted near the primary resonance point. It is shown that, in addition to the usual harmonic oscillation, two types of oscillations accompanying torsional modes are possible, whose amplitudes decrease in one type and increase in the other, as the excitation frequency increases. In this way the occurrence of the multi-mode response is ascertained. An experimental analysis is also conducted, which confirms the validity of the theoretical analysis.

ChemInform Abstract: STRUCTURE AND PREDISSOCIATION DYNAMICS OF ELECTRONICALLY EXCITED NITROGEN DIOXIDE: A RESONANCE RAMAN STUDY

Resonance Raman spectra of NO2 have been recorded as a function of excitation frequency in the range 0–8000 cm−1 above the predissociation threshold. These spectra are interpreted using the time‐dependent formulation of resonant Raman scattering, to elucidate the shape of the excited electronic state potential energy surface, and the dynamics which occur on it immediately following photoexcitation. Our results show that the dominant optical transition in this spectral range is 2B2–2A1. Our Raman spectra reveal a marked decrease in the dynamical time scale of the predissociation of the 2B2 state as excitation frequency increases. At excitation frequencies approximately 4850 cm−1 above the dissociation threshold, the 2B2 predissociative lifetime becomes comparable to a vibrational period. We have analyzed the resonance Raman spectra, along with the absorption spectrum, to determine the magnitudes of the slopes of the potential surface along the symmetric stretch and bending normal coordinates for the 2B2 ex...

Two-photon excitation spectroscopy and excited state decay kinetics of isolated diphenylbutadiene

We report the two-photon excitation spectrum and decay kinetics of the two-photon prepared states for diphenylbutadiene in a helium free jet. The spectrum is that of a symmetry allowed two-photon transition and is assigned using 17 harmonic fundamentals. A reexamination of the previously reported one-photon excitation spectrum allows the assignment of several additional u symmetry fundamentals of diphenylbutadiene’s excited 1Ag state. Curves of intensity vs time for light detected at two times the wave number frequency of the laser minus a Stoke’s shift of between 1000 and 9000 cm−1 show two components. One, due to two-photon resonance enhanced hyper-Raman scattering, reproduces the temporal profile of the exciting laser. The other, due to fluorescence from the excited 1Ag state, decays exponentially. The fluorescence lifetime decreases with increasing excitation frequency from 100 ns for 0–0 band excitation to 13 ns for excitation at 1235 cm−1 above the origin, consistent with the onset of a nonradiative decay channel previously observed for diphenylbutadiene in one-photon studies. Above this energy only hyper-Raman scattering is detected.

Structure and predissociation dynamics of electronically excited nitrogen dioxide: A resonance Raman study

Resonance Raman spectra of NO2 have been recorded as a function of excitation frequency in the range 0–8000 cm−1 above the predissociation threshold. These spectra are interpreted using the time-dependent formulation of resonant Raman scattering, to elucidate the shape of the excited electronic state potential energy surface, and the dynamics which occur on it immediately following photoexcitation. Our results show that the dominant optical transition in this spectral range is 2B2–2A1. Our Raman spectra reveal a marked decrease in the dynamical time scale of the predissociation of the 2B2 state as excitation frequency increases. At excitation frequencies approximately 4850 cm−1 above the dissociation threshold, the 2B2 predissociative lifetime becomes comparable to a vibrational period. We have analyzed the resonance Raman spectra, along with the absorption spectrum, to determine the magnitudes of the slopes of the potential surface along the symmetric stretch and bending normal coordinates for the 2B2 excited state in the Frank–Condon region.

Resonant Raman scattering from screened longitudinal optical phonons in EuTe

Forbidden resonant Raman scattering from screened longitudinal optical, LO, phonons has been observed in the back-reflection geometry from n-type EuTe at 2°K. The Raman shift increased with increasing excitation frequency but was always between the LO and TO phonon frequencies. This effect is explained in terms of a varying ‘effective’ carrier concentration as a function of laser penetration depth through the surface depletion layer in the situation of large phonon wave vector. Conduction band and lattice parameters have been calculated from infrared Reststrahlen and plasma edge measurements.