Relative Power Density Research Articles

DC and low-frequency noise characteristics of SiGe p-channel FETs designed for 0.13-μm technology

The impact of hole confinement on the DC and low frequency noise in SiGe p-channel FETs is investigated by comparison with Si p-FETs produced by the same technology. The relative spectral power density of low frequency (1/f) noise in SiGe pFETs is found to be significantly lower than in Si devices. This is mainly attributed to the physical separation of the holes confined in the SiGe channel from the Si/SiO/sub 2/ interface. The low value of SiGe channel noise proves the good quality of epilayers and heterointerfaces, as also revealed by the TEM cross section.

Light power density distribution of image spot of laser triangulation measuring

HaiMing Wang [Wang HaiMing, Long range optical triangulation utilising collimated probe beam. Optics and Lasers in Engineering, 23(11), 1995, 41–52] studied the influences of the size of the object spot on the image spot in laser triangulation measuring. This paper points out that the study method of HaiMing Wang is inappropriate from two points of view. The size and relative power density distribution of the image spot can be calculated either when assuming the object spot is an ideal point, which emits a uniform spherical wave over the object, or when assuming that the object surface is a light scattering surface. Both the conditions show that the size of the image spot is much bigger than that of HaiMing Wang’s.

Etching of Si at low temperatures using a SF6 reactive ion beam: Effect of the ion energy and current density

Reactive ion beam etching of silicon is performed at low substrate temperature (153<T<300 K). The beam is extracted from a SF6 microwave plasma. The energy of the beam is 100 eV<E<400 eV, the ion current density is 0<J<5 mA cm−2. Energy distribution and composition of the beam have been studied using a mass spectrometer coupled with a cylindric mirror analyzer. The beam can be considered as monoenergetic with a full width at half-maximum about 8 eV. Using SF6 plasma, F+ is the predominant species, a significant proportion of SF+, SF2+, S+, and SF3+ ions is present in the beam. The active neutral flux of fluorine atoms coming from the ion source has been estimated between 6×1016 and 4×1017 cm−2 s−1. When no ion beam strikes the sample, the probability of reaction of neutral F atoms with Si is evaluated between 0.02 and 0.1 at 300 K. The decrease of the substrate temperature has revealed the role of the ion-induced reaction and the ion-stimulated desorption of SFx radicals in the etching process. At relative low power densities (100<E<400 eV and J=0.65 mA cm−2), an increase in the etch yield occurs as the temperature decreases until 220 K because there is an enhancement of the ion-induced reactions. If the energy of the beam is not high enough, the etching is reduced or even blocked by a thick layer of adsorbed molecules at T<220 K. At higher power densities (100<E<400 eV and 2 mA cm−2<J<5 mA cm−2) no significant etch yield enhancement is noted as the temperature decreases because the ion-stimulated desorption becomes predominant. In the case of high current density which corresponds to low values of the ratio of neutral flux over ion flux (a few ten), the etch yield approaches the value of the physical sputtering yield calculated by a model derived from the Sigmund cascade collision.

Radiation characteristics of a meander-line dipole antenna

A simple analytical method is proposed for calculation of the vertically polarized and horizontally polarized relative power densities of a meander-line dipole (MLD) antenna. A sinusoidal distribution of current that drops to zero at both ends of the dipole is assumed. Results obtained using this method are in good agreement with results computed using the Numerical Electromagnetic Code [1]. The MLD antenna has some cross-polarization, which, for a constant antenna length, can be minimized by increasing the number of meander sections. The gain of the antenna is calculated as a function of antenna length with the number of meander sections as a parameter. The gain for the MLD antenna is greater than that for a straight-wire dipole of the same length.

Transurethral balloon laser thermotherapy: effects of a directionally shielded balloon in canine prostates.

Transurethral balloon laser thermotherapy (TUBAL-T) improves objective, but not subjective, symptoms of benign prostatic hyperplasia (BPH). We studied whether or not an Nd:YAG laser beam with a shielded balloon could successfully irradiate the prostate during TUBAL-T in selective manner, to improve the subjective symptoms. TUBAL-T was performed on canine prostates using the balloon with a laser probe, which was shielded anteriorly at 90 degrees (from the center of the balloon) and posteriorly at 90 degrees. At 20 watts laser power, the relative power density in the bilateral non-shielded areas was 17.4 and 17.8, and in the shielded area it was 1.0. Observation by thermography revealed that the temperature after laser radiation in a non-shielded area of a fish cake phantom was higher than in a shielded area. Following transurethral thermotherapy using a shielded balloon in dogs, a cavity was formed bilaterally around the urethra, and the tissues at the anteroposterior sides and the urethra were preserved. TUBAL-T, which has been performed in clinical cases of benign prostatic hyperplasia, might be useful in selective irradiation of adenoma if a shielded balloon is used.

Increasing the accuracy of laser beam diameter measurement

A procedure for determining the diameter of a focused laser beam based on the measurement of laser damage to a thin film is described. This method has several advantages over the spatial methods of using calibrated diaphragms and the measurement of relative power density distribution with subapertures.

Influence of lamotrigine addition on computerized background EEG parameters in severe epileptogenic encephalopathies.

In 12 adults with typical Lennox-Gastaut syndrome and partial epilepsies with secondary bilateral synchrony unsatisfactorily controlled by current antiepileptic drugs, the following computerized background EEG parameters were studied before and during beneficial antiepileptic effect of lamotrigine addition: absolute and relative spectral power density; alpha/theta index; dominant frequency of occipital alpha, theta and delta bands. The only significant influence of lamotrigine addition was a moderate decrease of the median and mean absolute delta power (p < 0.01). We concluded there was a poor influence of therapeutic doses of lamotrigine on the background diffuse slow dysrhythmias characteristic to severe early encephalopathies which engender both severe secondary epilepsies and different degrees of mental handicap.

Infrared surface waves in circular hollow waveguides with small core diameters

An asymptotic form of the characteristic equation that describes wave propagation at near-infrared wavelengths in small core hollow circular waveguides is developed. Analytic solutions for the transverse and axial propagation constants are obtained. These demonstrate the transition of the TE/sub 11/ and TM/sub 01/ modes to surface waves as the guide radius is increased to values much greater than at cutoff. Relative power density distributions illustrating these mode transitions are shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of polarization fluctuations in installed single-mode optical fibre cables

Measurements were made of the random polarization fluctuations of conventional single-mode fibres of five optical fibre cables installed in the city of Berlin (West). The measurements were performed with the aid of a semiconductor laser, the frequency (f) of which was 227.3 THz (wavelength 1320 nm). Such preliminary studies are very important for optically coherent transmission over cables not maintaining the polarizations. The signal intensity fluctuations as the fibre output can be represented both as a function of time and by the related spectral power density.

Analysis of the transferred-electron effect in the InGaAsP system

The transferred-electron effect in the quaternary system InGaAsP is investigated. The main points of interest are the threshold field and the peak velocity at the onset of electron transfer. They are determined from a monoenergetic transport model giving basic understanding of electron dynamics. In addition, the frequency limit, the efficiency of microwave generation and the related power density are discussed. Physical insight into the prevailing mechanisms of high-field electron transport is obtained by comparing the theoretically estimated frequency limit and the length of the inactive zone derived from experiment. Based on these results the most promising alloys of this quaternary system are discussed in more detail to specify their range of applicability.

Efficient and accurate method for calculating and representing power density in the near zone of microwave antennas

A method for computing and exhibiting Fresnel-region fields radiated by microwave antennas that uses plane-wave scattering matrix analysis is presented. Near-fields are calculated by numerically integrating the complex far-field antenna pattern. The predicted near fields are exhibited as relative power density contours lying in a longitudinal plane bisecting the antenna's aperture. With spatial-coordinate scaling, each set of contours becomes a function of the relative aperture distribution and the electrical size of the antenna. If the electrical diameter is much larger than any normalized transverse coordinate of interest, the contour set becomes invariant with respect to antenna size. The coordinate normalization can produce contours applicable to any antenna with the same relative aperture distribution, regardless of antenna size.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of thin-film optical absorption at the air-film interface within the film and at the film-substrate interface

A measurement technique is described where the absorption introduced by the addition of a single-layer thin film is separated into three parts: absorption (a) within the bulk of the film; (b) at the air-film interface; (c) at the film-substrate interface. The technique employs a scanning adiabatic calorimeter to measure substrates which are partially coated on the entrance surface with films of continuously varying thickness. By measuring the absorption on the bare substrate and at various film thicknesses, and by making use of changes in relative power density within the film for λ/4 versus λ/2 optical thickness films, we have determined (a) αf, the bulk absorption coefficient of the film, (b) aaf, the specific absorptance of the air-film interface, and (c) afs, the specific absorptance of the film-substrate interface. The analysis assumes that the films are highly transparent and of known index of refraction. In addition, the film thickness must range from λ/4 to 3λ/4 optical thickness, or from λ/2 to λ optical thickness. Representative data are shown for absorptance measurements at 2.7 and 2.9 μm for a film of As2Se3 on CaF2. This example exhibits predominantly film-substrate interface absorption with very little of the absorption taking place in the bulk of the film.

Comparison of the Power Distribution in Uranium and Plutonium Fuel Elements in the KWO Core

The introduction of plutonium-charged fuel elements was investigated with regard to a change in the axial power density distribution. An attempt was made to gather information regarding the influence of coolant temperature change on the local power production. The state of the reactor during the investigations was supposed to correspond to realistic operating conditions. During stretch-out operation, as a result of the reduction of the mean coolant temperature and the reactor power, the fall in coolant outlet temperature is greater than the rise in inlet temperature. Hence, the greatest coolant density change occurs at the coolant outlet. In this manner, the relative power density distribution is displaced toward the upper core half. In a special experiment, the influence of turbine load changes on the axial power density distribution in a noncontrolled reactor was investigated. A power reduction at the turbine causes a rise in the mean coolant temperature of the reactor. Owing to local coolant temperature differences, the power density was found to displace toward the upper core half in a noncontrolled reactor, this being more so the case for plutonium fuel elements. The investigations cited in this report and the good agreement between the theoretical predictions and the experimentsmore » permitted the recycling of the self-bred plutonium at KWO without restrictions on the operation of the reactor.« less

Optimum coherent imaging of a limited field of view in the presence of angular and aperture noise

An optimal procedure is established for the reconstruction of the angular object distribution in a given field of view (FOV). The object is coherently illuminated and located in the far zone of the receiving aperture. The procedure is “uniformly” optimal in the sense of minimizing the statistical r.m.s. difference between the object distribution, modeled as a random function of the angular coordinates and its reconstructed image, for each direction belonging to the FOV. The observable complex amplitude distribution of the field on the aperture is due in the general case not only to the incidentfield scattered by the object but also to background disturbance, or “angular noise”, randomly distributed inside and outside the FOV, and is affected by “measurement noise”, that is random errors introduced in measuring the aperture field. The reconstruction algorithm consists of summing a truncated series of special functions—prolate spheroidal for the linear case and their generalizations for two dimensional apertures—weighted by appropriate coefficients. These coefficients depend upon the observed aperture field and upon the relative power densities associated with the object field and the various types of noise. The series is truncated to a number of terms (“effective degrees of freedom” of the image) determined through an information theoretical method: each term of the series, suitably ordered, provides an information gain less than the preceding one, and the information gain goes rapidly to zero. A relationship between information transfer and mean squared error for each term in the image series is established. Numerical examples are discussed.

A test and research reactor excursion radiation detection system using an on-line computer

A pulse reactor radiation detection system is described. The system uses an on-line Scientific Data Systems (SDS) 920 computer, coupled through an analog to digital converting interface, to record and retain the response data for various radiation detectors. Results of typical measurements are presented. An overall range of sensitivity of 10 6 is possible with a precision to within about 5% (exclusive of the detectors) for determining relative reactor power, neutron and gamma ray flux densities (if the spectra remain constant), and neutron and gamma ray tissue kerma rates or the time integral of these quantities. This range is achieved using combinations of radiation sensors.

Power Density Diagrams of Short-Wave Aerial Arrays

This paper outlines a method of obtaining the distribution in space of the power radiated from short-wave arrays of horizontal elements. The method utilizes the radiation properties of a system of point-sources to which an array may be reduced, together with the directional characteristics of the simple half-wave dipole, the basic element of which the array is composed.A chart is presented which gives on the framework of the power distribution diagram, contours that correspond to the paths traversed in space by points with a fixed directivity so far as factors dependent on the horizontal spread caused by horizontal radiating elements are concerned. The chart is directly useful in obtaining the final value of the relative power density at all points in space.