Experimental Measurements Of Attenuation Research Articles

Effect of Vertical Downdraft on Rain Attenuation Modeling Over an Earth-Space Path

The impact of vertical downdraft on rain attenuation estimation from rain rate measurements has been studied. The rain rate (<i>R</i>) and specific attenuation (&#x03B3;) are derived from rain drop size distributions (DSD) by considering the widely accepted Gunn&#x2013;Kinzer (G-K) relationship between drop size and drop fall velocity that is valid for stagnant air. In the real atmosphere, drops are carried with the vertical wind draft, and the actual fall velocity of the raindrops deviates from the G&#x2013;K formulation. The ITU-R estimated rain attenuation values, based on DSDs, which are mostly valid for temperate regions, can deviate from actual rain attenuation measurements in tropical regions, especially at higher rain rates when downdraft is prominent. The present study uses disdrometer measurements of DSD, optical rain gauge measurements of rain rates, and Ku-band rain attenuation data over an earth-space path at a tropical location Kolkata (22&#x00B0;34&#x2032; N, 88&#x00B0;29&#x2032; E) to show that vertical downdrafts impact the rain attenuation estimation from rain rate measurements. At the present location, an overall representative vertical downdraft of 2 m&#x002F;s needs to be considered to match the experimental attenuation measurements with the estimated values using the modified &#x03B3;&#x2013;<i>R</i> relationship in the ITU-R model.

Experimental Measurements of Attenuation and Recovery within Single Mode Optical Fiber Cables under the Effects of Gamma Radiation

Efficient transmission of data within optical fiber cables within radiation environments is a challenge. It leads to severe attenuations in the optical fiber cables. This issue is addressed in this manuscript. Experimental measurements are conducted in order to overcome the radiation influence on single mode optical fiber cables. Two experiments are implemented. The first one depends on 5 m single mode patch cords fiber cable. This cable is subjected to gamma radiation

The Effect of Attenuation from Fish on Passive Detection of Sound Sources in Ocean Waveguide Environments

Attenuation from fish can reduce the intensity of acoustic signals and significantly decrease detection range for long-range passive sensing of manmade vehicles, geophysical phenomena, and vocalizing marine life. The effect of attenuation from herring shoals on the Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) of surface vessels is investigated here, where concurrent wide-area active Ocean Acoustic Waveguide Remote Sensing (OAWRS) is used to confirm that herring shoals occluding the propagation path are responsible for measured reductions in ship radiated sound and corresponding detection losses. Reductions in the intensity of ship-radiated sound are predicted using a formulation for acoustic attenuation through inhomogeneities in an ocean waveguide that has been previously shown to be consistent with experimental measurements of attenuation from fish in active OAWRS transmissions. The predictions of the waveguide attenuation formulation are in agreement with measured reductions from attenuation, where the position, size, and population density of the fish groups are characterized using OAWRS imagery as well as in situ echosounder measurements of the specific shoals occluding the propagation path. Experimental measurements of attenuation presented here confirm previous theoretical predictions that common heuristic formulations employing free space scattering assumptions can be in significant error. Waveguide scattering and propagation theory is found to be necessary for accurate predictions.

Three-dimensional modeling of Lamb wave attenuation due to material and geometry in composite laminates

When a Lamb wave propagates in a three dimensional (3D) domain, attenuation i.e. reduction in amplitude of the wave with distance of propagation is due to geometry and material. Experimental measurements of attenuation of a Lamb wave consist of both the effects of geometry and material as well. In the present work, a technique to estimate the attenuation due to material from combined attenuation (geometry and material) was proposed. The estimated material attenuation coefficient was then used in 3D numerical simulations of Lamb wave to capture the combined attenuation. The proposed technique was verified through numerical simulations followed by experimentally measured data on a composite laminate. Furthermore, the entire distance of propagation of a Lamb wave was classified into three regions based on attenuation characteristics.

Wireless Transmission in Tunnels With Non-Circular Cross Section

We study wireless communication via the free modes in a uniform tunnel with non-circular cross section. The dominant modes propagating in such tunnel are considered as perturbed versions of corresponding modes in the well studied circular tunnels. Of particular practical interest are tunnels whose cross section comprise an incomplete circle with flattened base. It is shown that in these tunnels, a vertically polarized mode is more attenuated than its horizontally polarized counterpart. We also investigate the approximation of a non-circular tunnel with an equivalent rectangular tunnel regarding the attenuation of the dominant modes. Comparison is made with experimental attenuation measurements available in the literature.

Estimation of adhesive bond strength in laminated safety glass using guided mechanical waves: Part II. An attenuation approach

Estimation of adhesive bond strength in laminated safety glass samples, ie windshields, has been carried out using a multilayered guided wave model and validated using attenuation measurements. As in Part I of this study, the interfaces are treated as imperfect interfaces and modelled as beds of longitudinal and shear springs. The spring constants are estimated using fracture mechanics in conjunction with surface analysis of the plastic interlayer and glass plates via atomic force microscopy and profilometer measurements. Using the multilayered guided wave model, it was observed that the S 1 mode exhibits periodic attenuation peaks in specific frequency ranges, and that the attenuation of these peaks is sensitive to the interface adhesion levels. The mode shapes and power flow profiles corresponding to these peaks are presented and discussed. Experimental attenuation measurements taken on the same laminated safety glass test samples discussed in Part I are presented and discussed to validate the theoretical predicted attenuation values using this multilayered model.

Acoustic performance of a Herschel–Quincke tube modified with an interconnecting pipe

The classical two-duct Herschel–Quincke tube is modified by means of an additional pipe connecting both paths. A transfer matrix is obtained for a mesh system with five arbitrary branches and then particularized to the proposed scheme. Experimental attenuation measurements were performed on several prototypes, and the results compared favourably with predictions from the previous theoretical development. Finally, transmission loss contour plots were used to study the influence of the connecting pipe on the resonance frequencies. The results confirm the nontrivial character of the influence observed, and simple relationships are obtained for the general trends.

An attenuation-based sediment classification technique using Chirp sub-bottom profiler data and laboratory acoustic analysis

A remote sediment classification technique based on attenuation measurements from Chirp sub-bottom profiler data is described. This differs from previously published work in that attenuation measurements are obtained for each stratigraphic unit within a complex, thinly interbedded sedimentary sequence. Compressional wave attenuation measurements are obtained for a wide variety of lithologies, including muds, silts, sands, clayey sands, silty clays and gravel lags, with grain sizes ranging from 8 Phi to -4 Phi. In addition, attenuation measurements from sub-bottom profiler data were calibrated against laboratory acoustic measurements of vibracores and seabed samples from corresponding geographic locations, under simulated in-situ conditions using a Pulse Tube method. We adapt an instantaneous frequency matching method using a causal attenuation filter to model the decay of the Chirp transmitted waveform. From this modelling, a relationship between t* (a causal attenuation operator) and change in instantaneous frequency is established. The Hilbert transform is used to extract instantaneous frequency information from Chirp seismic, which is used to derive attenuation information for selected individual stratigraphic layers imaged by the sub-bottom profiler. This paper draws attention to the limitations in comparing attenuation measurements derived from Chirp sub-bottom profiler data against previously published literature on experimental attenuation measurements, which are limited by the wide variance of these data, and the difficulty in finding a meaningful best fit to these data. This demonstrates the importance of calibrating remote sediment classification observations using complimentary acoustic analysis of seabed samples to generate a site-specific geoacoustic database. A positive correlation between laboratory and sub-bottom profiler attenuation measurements was obtained, with a correlation coefficient of 0.885. Poorly sorted gravels with a mixed lithic and biogenic pebble component are characterised by very high attenuation with values of Q from 4 to 19. These sediments are considerably coarser-grained than those typically described in previously published experimental studies.

Adaptive Neural Network for Nuclear Medicine Image Restoration

A novel adaptive neural network is proposed for image restoration using a nuclear medicine gamma camera based on the point spread function of measured system. The objective is to restore image degradation due to photon scattering and collimator photon penetration with the gamma camera and allow improved quantitative external measurements of radionuclidesin-vivo . The specific clinical model proposed is the imaging of bremsstrahlung radiation using ^32P and^90 Y because of the enhanced image degradation effects of photon scattering, photon penetration and poor signal/noise ratio in measurements of this type with the gamma camera. This algorithm model avoids the common inverse problem associated with other image restoration filters such as the Wiener filter. The relative performance of the adaptive NN for image restoration is compared to a previously reported order statistic neural network hybrid (OSNNH) filter by these investigators, a traditional Weiner filter and a modified Hopfield neural network using simulated degraded images with different noise levels. Quantitative metrics such as the change of signal to noise ratio (ΔSNR) are used to compare filter performance. The adaptive NN yields comparable results for image restoration with a slightly better performance for the images with higher noise level as often encountered in bremsstrahlung detection with the gamma camera. Experimental attenuation measurements were also performed in a water tank using two radionuclides, ^32P and ^90 Y, typically used for antibody therapy. Similar values for an effective attenuation coefficient was observed for the restored images using the OSNNH filters and adaptive NN which demonstrate that the restoration filters preserves the total counts in the image as required for quantitative in-vivo measurements. The adaptive NN was computationally more efficient by a factor 4–6 compared to the OSNNH filter. The filter architecture, in turn, is also optimum for parallel processing or VLSI implementation as required for planar and particularly for tomographic mode of detection using the gamma camera. The proposed adaptive NN method should also prove to be useful for quantitative imaging of single photon emitters for other nuclear medicine tomographic imaging applications using positron emitters and direct X-ray photon detection.

Squirt flow in fully saturated rocks

We estimate velocity/frequency dispersion and attenuation in fully saturated rocks by employing the squirt‐flow mechanism of solid/fluid interaction. In this model, pore fluid is squeezed from thin soft cracks into the surrounding large pores. Information about the compliance of these soft cracks at low confining pressures is extracted from high‐pressure velocity data. The frequency dependence of squirt‐induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space, and the characteristic squirt‐flow length. These unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency. The appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity. The low‐frequency velocity limits, as given by our model, are identical to those predicted by Gassmann’s formula. The high‐frequency limits may significantly exceed those given by the Biot theory: the high‐frequency frame bulk modulus is close to that measured at high confining pressure. We have applied our model to D’Euville Limestone, Navajo Sandstone, and Westerly Granite. The model realistically predicts the observed velocity/frequency dispersion, and attenuation.

Effect of magnetic dissipation on propagation of dipole spin-wave envelope solitons in yttrium iron garnet films

The results of direct experimental measurements of attenuation of a spin wave envelope soliton propagating in a high-quality yttrium-iron-garnet (YIG) film ( Delta H=0.3 Oe) are presented. It is shown that the envelope soliton attenuation is approximately two times larger than attenuation of the linear sinusoidal signal in the same film.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Propagation of sound in highly porous open-cell elastic foams

This work presents both theoretical predictions and experimental measurements of attenuation and progressive phase constants of sound in open-cell, highly porous, elastic polyurethane foams. The foams are available commercially in graded pore sizes for which information about the static flow resistance, thermal time constant, volume porosity, dynamic structure factor, and speed of sound is known. The analysis is specialized to highly porous foams which can be efficient sound absorbers at audio frequencies. Negligible effect of internal wave coupling on attenuation and phase shift for the frequency range 16–6000 Hz was predicted and no experimentally significant effects were observed in the bulk samples studied. The agreement between predictions and measurements in bulk materials is excellent. The analysis is applicable to both the regular and compressed elastic open-cell foams.

Elastic behaviour of YAG under pressure

Measurements of the effects of hydrostatic and uniaxial pressures on ultrasonic wave velocities are used to obtain the six third-order elastic constants of yttrium aluminium garnet (YAG). Results are used to investigate whether the shear isotropy and the conformity with the Cauchy relation (indicative of central forces), which hold for the second-order elastic constants of YAG, extend into the region of finite strain which determines higher-order elasticity. The compression has been extrapolated up to 150*108 Pa using the Murnaghan equation of state. The vibrational anharmonicity of YAG and yttrium iron garnet (YIG) are compared through the acoustic-mode Gruneisen gammas computed from the pressure dependences of the elastic constants. The attenuation of transverse microwave ultrasonic waves propagated along the (001) direction (the mode used in acoustic devices) due to anharmonic interactions with thermal phonons, calculated at the limits omega tau >>1 and omega tau <1, is shown to be in good agreement with previous experimental attenuation measurements for this mode.

Measurement of normal incidence airborne sound transmission loss for open-plan office panels

A new laboratory test procedure is developed that evaluates the normal incidence sound transmission loss characteristics of a partial height panel. A comprehensive comparison of test data and the resulting single number ratings are made between the proposed and the existing barrier/sound transmission loss test procedures. Experimental attenuation measurements for various open-plan office configurations were in close agreement with calculated theoretical predictions using the geometrical theory of diffraction and normal incidence sound transmission loss test data. Measurements were conducted in a semi-anechoic room using a one-third octave band real time analyzer and pink noise as the test signal. The new test procedure provides one-third octave band data for complete acoustical analysis and a single number rating, called Weighted Articulation Index Average, for partial height panel comparisons.

The Attenuation of Love Waves and Toroidal Oscillations of the Earth

An attempt has been made to invert a large set of attenuation data for Love waves and toroidal oscillations in the earth, using a recent method by Backus and Gilbert. The difficulty in finding an acceptable model of internal friction which explains the data, under the assumption that the internal friction is independent of frequency, casts doubt on the validity of this assumption. A frequency-dependent model of internal friction is presented which is in good agreement with the seismic data and with recent experimental measurements of attenuation in rocks.

Cobalt 60 protection design.

The recent report by the National Committee on Radiation Protection, published as Bureau of Standards Handbook 54 (1) includes basic information on cobalt 60 teletherapy shielding. So far as experimental attenuation data for the primary and 90° scattered radiation are concerned, the Handbook is particularly complete; data based on experience with completed installations, however, are limited, since cobalt teletherapy is a rather recent development. It is the purpose of the present report to give this supplementary information. The study includes surveys of completed installations, the design of which was based on experimental attenuation measurements (2–4). In Figure 1 are shown schematically the three types of radiation which should be considered in protection design; the useful beam, scattered radiation, and leakage radiation. Since the intensity and energy of the scattered radiation vary with angle of scatter, size of field, etc., its attenuation presents the more difficult problem. The structural shielding requirements of teletherapy installations vary widely and depend on a number of factors, the most important of which are as follows: 1. Degree of occupancy of nearby regions. 2. Orientation of useful beam. 3. Type of equipment. 4. Weekly work load in r/week at 1 meter (in air). 1. Degree of Occupancy: Handbook 54 is the first protection code to give occupancy factors for areas of various types. This permits the designer to adjust the barrier thickness to meet actual requirements. A stairway, for instance, is assumed to be occupied not more than one-sixteenth of the time by the same personnel. Since an occupancy factor of 1/16 reduces the required thickness by four half-value layers, a primary concrete barrier is reduced by 10 inches. It is obvious, therefore, that significant savings can be gained by proper location of the teletherapy room with respect to occupancy of surrounding regions and by orientation of the equipment so that the beam is directed toward an outside wall. Where there is a possibility of a future increase in the degree of occupancy, it is more economical to provide for this originally. A corner room on the bottom floor, preferably below ground, usually requires minimum shielding. This does not necessarily mean minimum expense, since excavation may cost more than the required additional shielding. In some instances, it is more practical to locate the telecobalt room on an upper floor in order that it be close to existing x-ray therapy facilities. In such cases efficient shielding design is essential. This is not merely a matter of cost. Often the weight of the shielding determines whether an upper-floor location is feasible. 2. Orientation of Useful Beam: The most effective way of reducing the shielding cost and weight is by limiting orientation of the useful beam to actual requirements. Such restriction permits the use of secondary barriers of less thickness for all areas exposed only to scattered and leakage radiation.