Angular Power Distribution Research Articles

Frequency response in step index plastic optical fibers obtained from the generalized power flow equation

We present a method to obtain the frequency response of step index (SI) plastic optical fibers (POFs) based on the power flow equation generalized to incorporate the temporal dimension where the fibre diffusion and attenuation are functions of the propagation angle. To solve this equation we propose a fast implementation of the finite-difference method in matrix form. Our method is validated by comparing model predictions to experimental data. In addition, the model provides the space-time evolution of the angular power distribution when it is transmitted throughout the fibre which gives a detailed picture of the POFs capabilities for information transmission. Model predictions show that angular diffusion has a strong impact on temporal pulse widening with propagation.

Measurement of angular power profile at an array receiver in a shallow underwater acoustic channel

In the design of broadband underwater acoustic communication system, proper analysis of underwater acoustic channel characteristics is required to determine communication system parameters. Especially for high channel capacity transmissions such as multiinput multioutput (MIMO) systems, the spatial correlation characteristics among multiple sensors determine communication performance and they are affected by the angular power distribution of the incoming acoustic waves. In this study, we suggest a model‐based array signal processing technique for measuring the angular power profile and apply it to experimental data gathered from very shallow water of 20 to 30 m water depth near the southern coast of South Korea. At first we show the variation of the angular power profile over different transmitter/receiver ranges and then its impact on the spatial correlation characteristics between two different array elements. Finally we discuss the expected spatial diversity effects from the viewpoint of underwater acoustic channel modeling.

Special features of the angular distribution of synchrotron radiation power of descrete spectral harmonics

A review of new achievements in theoretical investigations of angular distribution of synchrotron radiation power is presented.

A soft x-ray beamline capable of canceling the performance impairment due to power absorbed on its optical elements

We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>10(4)) and spot size (4x4 microm2) at the sample position despite being exposed to more than 2.15 kW of undulator radiation and a maximum power density on the optics of more than 0.9 W/mm2. Ray tracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulator's central cone, which contains the usable photons but is considerably smaller than the angular power distribution.

Light extraction study of LED using ray tracing computer simulation

This paper presents optical simulation results of different types of compound semiconductor LEDs. Transmitted light power angular distribution and other important LED properties have been studied in order to define how exactly geometry, contacts, layers, coating or encapsulating can change major LED parameters in complex. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Estimation of soft X-ray and EUV transition radiation power emitted from the MIRRORCLE-type tabletop synchrotron

The tabletop synchrotron light sources MIRRORCLE-6X and MIRRORCLE-20SX, operating at electron energies E(el) = 6 MeV and E(el) = 20 MeV, respectively, can emit powerful transition radiation (TR) in the extreme ultraviolet (EUV) and the soft X-ray regions. To clarify the applicability of these soft X-ray and EUV sources, the total TR power has been determined. A TR experiment was performed using a 385 nm-thick Al foil target in MIRRORCLE-6X. The angular distribution of the emitted power was measured using a detector assembly based on an NE102 scintillator, an optical bundle and a photomultiplier. The maximal measured total TR power for MIRRORCLE-6X is P(max) approximately equal 2.95 mW at full power operation. Introduction of an analytical expression for the lifetime of the electron beam allows calculation of the emitted TR power by a tabletop synchrotron light source. Using the above measurement result, and the theoretically determined ratio between the TR power for MIRRORCLE-6X and MIRRORCLE-20SX, the total TR power for MIRRORCLE-20SX can be obtained. The one-foil TR target thickness is optimized for the 20 MeV electron energy. P(max) approximately equal 810 mW for MIRRORCLE-20SX is obtained with a single foil of 240 nm-thick Be target. The emitted bremsstrahlung is negligible with respect to the emitted TR for optimized TR targets. From a theoretically known TR spectrum it is concluded that MIRRORCLE-20SX can emit 150 mW of photons with E > 500 eV, which makes it applicable as a source for performing X-ray lithography. The average wavelength, \overline\lambda = 13.6 nm, of the TR emission of MIRRORCLE-20SX, with a 200 nm Al target, could provide of the order of 1 W EUV.

Effect of Antenna Directivity on Angular Power Distribution at Mobile Terminal in Urban Macrocells: A Geometric Channel Modeling Approach

We present a geometric channel model to study the effect of antenna directivity on angular power distribution at the mobile terminal in urban macrocells. The methodology reviewed in this paper integrates the antenna effect into the model geometry, thereby facilitating a system-dependent channel characterization. As each device is limited in terms of measurement sensitivity, the effective scatterer distribution is essentially dependent on the antenna beam pattern. Subsequently, two heuristic rules are proposed to establish the underlying relationship between the model geometry and the corresponding wave-propagation processes. It is shown that the influence of directional antenna is twofold. First, it alters the spatial distribution of scatterers by providing a different sample space for the random field, and secondly, it distributes signal components into the angles-of-departure or collects them from the angles-of-arrival by weighted combination. Important channel parameters measured at the mobile terminal such as the angular power distribution, Doppler spectrum, and multipath shape factors are also investigated to further exemplify the usefulness of the proposed model.

Maximizing<tex>$hbox Alq_3$</tex>OLED Internal and External Efficiencies: Charge Balanced Device Structure and Color Conversion Outcoupling Lenses

In this paper, we report bright, efficient Alq3-based [tris-(8-hydroxyquinoline) aluminum] organic light-emitting diode (OLED) structures that incorporate hemispherical lenses for increased output power efficiency. The 6-layer hybrid (polymer/small molecule) OLED structure contains two spin-coated polymer layers and four thermally evaporated small molecule layers. This structure results in balanced charge injection, thus leading to a more efficient device. The use of index-matched transparent lenses resulted in luminous and external quantum efficiency of 7.5 lm/W and 8%, respectively. The size and shape of the lens was used to control the angular power distribution. Lenses incorporating color conversion media were used to achieve high OLED efficiency in various colors. Saturated yellow, orange, and red devices with external quantum efficiencies as high ~4% were obtained from this approach

Effect of Distribution Pattern of Molecular Dipoles onMicroscopic Second-Harmonic Generation

We set up a model for dealing with the second-harmonic generation (SHG)from molecular dipoles in a line alignment pattern rather than a planardistribution under a microscope. Because of this model, it is possibleto perform a flexibly quantitative investigation of SHG from collagenfibres at a molecular level. The line alignment pattern induces moresignificant modifications in both the angular dipole distributionstructure A(θ,φ) and the second-harmonic power structureΘy(θ,φ), compared to a planar distribution. Also, the linealignment angle t has strong effect on A(θ,φ) andΘy(θ,φ), resulting in an irregular SHG angular powerdistribution. That is to say, it is unnecessary for SHG emission topresent two well-defined off-axis lobes. The total SHG power shows twosymmetrical peaks at angles of t = 50° and t = 130° while a drop at t = 90°. The weakest SHGsignals can be measured at t = 0° and t = 180°.

Characteristics of synchrotron radiation and the structure of the permanent magnetic wiggler

The general characteristics of the synchrotron radiation of the permanent magnetic wiggler, and the angular distribution of power and total power radiated for the permanent magnetic wiggler are introduced briefly. After briefly describing the basic structure of the permanent magnetic wiggler, we report the procedure of applying the finite element analysis to the C-shape frame and the integral structure which are the main bearer of the load,in order to determine the displacement of structure of magnet under different conditions. The displacement of the C-shape frame is calculated by the theoretical formula to provide a theoretical basis for further structure design and improvement of the permanent magnetic wiggler.

Some properties of the angular power distribution of electromagnetic waves multiply scattered in a collisional magnetized turbulent plasma

A study is made of oblique incidence of a small-amplitude plane electromagnetic wave on a semi-infinite slab of a collisional turbulent plasma in an external uniform magnetic field. In the small-angle scattering approximation, the condition for neutralizing the effects of oblique incidence and plasma anisotropy on the statistical properties of radiation multiply scattered in the absorbing plasma medium is determined by using the methods of geometrical optics. The validity of this condition was confirmed by numerical calculations based on the statistical modeling technique. The effect of the shape of the spectrum of the electron density fluctuations on the shape of the angular power distribution of a multiply scattered radiation is investigated.

Design of mode scramblers for step-index and graded-index plastic optical fibers

We analyze the internal evolution of light power angular distribution in typical mode scrambling configurations by comparing the resultant far fields, obtained either experimentally or computationally, with the experimental equilibrium mode distribution (EMD) far field for the plastic optical fibers (POF) considered, so as to provide an insight that helps to adapt existing scramblers to new types of POF that are coming onto the market.

Evolution of the angular power spectrum of scattered radiation from a point source upon propagation in a turbid medium

The propagation of radiation from a point source through a plane layer of an absorbing medium with smooth random permittivity inhomogeneities is considered for the case in which the source and a receiver are spaced by different distances from the layer boundaries. The angular power spectra of the scattered radiation are calculated by the method of statistical modeling for different values of the layer thickness, positions of the source and the receiver relative to the layer, and absorption in the layer. The results for the moments of the angular power distribution obtained earlier in the small-angle approximation are fully confirmed. The transformation of the angular power spectrum upon variation of the source or receiver position with respect to the layer is analyzed for the first time.

Highly directive radiation from sources embedded inside photonic crystals

In this work, we have experimentally and theoretically studied the angular distribution of power emitted from a radiation source embedded inside a photonic crystal. Our results show that it is possible to obtain highly directive radiation sources operating at the band edge of the photonic crystal. Half power beam widths as small as 6° have been obtained. Our results also show that the angular distribution of power strongly depends on the frequency and on the size of the photonic crystal.

Angular power distribution and mean effective gain of mobile antenna in different propagation environments

We measured the elevation angle distribution and cross-polarization power ratio of the incident power at a mobile station in different radio propagation environments at 2.15 GHz frequency. A novel measurement technique was utilized, based on a wideband channel sounder and a spherical dual-polarized antenna array at the receiver. Data were collected over 9 km of continuous measurement routes, both indoor and outdoor. Our results show that in non-line-of-sight situations, the power distribution in elevation has a shape of a double-sided exponential function, with different slopes on the negative and positive sides of the peak. The slopes and the peak elevation angle depend on the environment and base-station antenna height. The cross-polarization power ratio varied within 6.6 and 11.4 dB, being lowest for indoor and highest for urban microcell environments. We applied the experimental data for analysis of the mean effective gain (MEG) of several mobile handset antenna configurations, with and without the user's head. The obtained MEG values varied from approximately -5 dBi in free space to less than -11 dBi beside the head model. These values are considerably lower than what is typically used in system specifications. The result shows that considering only the maximum gain or total efficiency of the antenna is not enough to describe its performance in practical operating conditions. For most antennas, the environment type has little effect on the MEG, but clear differences exist between antennas. The effect of the user's head on the MEG depends on the antenna type and on which side of the head the user holds the handset.

Direction‐of‐arrival statistics of urban propagation channel at 1.9 GHz based on measurement and ray tracing

AbstractThe statistics of direction of arrival (DOA) in an urban environment are generated based on measurement and ray tracing simulation. The angular power distributions at different locations of the city are fit into the Gaussian angle‐of‐arrival model. The following four quantities are then extracted as model parameters: The number of incoming DOA, the normalized amplitude of each incoming signal, the mean direction of the incoming signals, and the standard deviation of the incoming signals about the mean direction. It is shown that the statistics of the above four quantities resulting from the simulation are in good agreement with those from the measurement data. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 31–35, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10364

Method for estimating the distance of an acoustic signal

A system and method for detecting the range of an acoustic source within a reverberant space. The invention includes a method, apparatus, and computer program to determine whether a sound source is situated near or far from a pair of microphones situated within a reverberant space. A signal detector is applied to the data; only the data that passes the signal detector is processed any further. The signal at the two microphones is compared to obtain the angular distribution of acoustic power. The concentration of acoustic power in the direct path versus reverberant paths is determined and used to compute a direct-to-reverberant ratio. If this ratio is greater than a selected threshold, the sound source is determined to be near the microphones. Otherwise, the sound source is determined to be far from the microphones.

Directivity of a Spherical Two-Mirror Antenna with an Extended Infrared Receiver

Some characteristics of Cassegrain optical systems, consisting of two spherical mirrors, are considered. Based on simulations in the geometric-optical approximation for a wide range of parameters, we find the relationship between the geometry of an optical system with an extended thermal receiver and the main-lobe width of the angular distribution of the system power. This permits one to optimize the system design on the basis of its performance requirements. We determine the optimal displacement of the small mirror from the quasi-focal area of the large mirror, ensuring the minimum main-lobe width in terms of a given level and a given dissipation factor.

Simulation of short LSAW transducers including electrode mass loading and finite finger resistance.

The theory for the 2-D numerical analysis of acoustic wave generation from finite length leaky surface acoustic wave (LSAW) transducer structures is presented. The mass loading of the electrodes is incorporated through the use of the finite element method (FEM). The substrate is modeled using both analytical and numerical means. The advantages of this simulation are twofold. First, it is capable of extracting the individual bulk wave conductances from the overall conductance of a given device. At large distances from the transducer, the angular distribution of power radiated relative to the substrate surface can then be calculated for each of the three possible bulk wave polarizations. The second advantage of the simulation is that the effect of finite electrode resistance is included through the use of a series equivalent resistance for each electrode in the structure. Once the resistance for each electrode in the structure has been determined, the overall effect on the device admittance is modeled by applying a constrained minimization process to the electrical boundary conditions of the transducer. To conclude the paper, the simulation will be compared against the experimental admittance of a 37-finger uniform transducer with a metalization ratio of 0.5 on 42 degrees LiTaO3. The agreement between theory and experiment is excellent.

A method of accurate determination of azimuthal distribution of received RF power

AbstractIn this paper, we introduce a method for the determination of directional distribution of received RF power, with angular resolution independent of receiving antenna radiation pattern. The proposed method is based on a series of measurements taken while rotating, at fixed predefined steps, a usual directional antenna of known radiation pattern on the azimuthal plain. It is proved that the resolution accuracy of the measurement method depends only on the angular step of the antenna rotation and it is independent of the antenna beamwidth. As a result of this feature, the proposed method allows the determination of the RF power angular distribution with fine resolution using a directional antenna of much wider beamwidth for the measurements. Copyright © 2001 John Wiley & Sons, Ltd.