Spatial Distribution Of Absorption Research Articles

Spatial distribution of absorption in plasmonic thin film solar cells

The spatial dependence of absorption in a structured thin film solar cell is investigated through the rigorous coupled-wave analysis method. The investigated structure allows strong localized surface plasmon and surface plasmon polaritons, simultaneously. The absorptance of silver and amorphous silicon can be separately accounted for by calculating the time-averaged energy dissipation although only the absorption of amorphous silicon contributes to the photocurrent. In our studied case, the metallic material absorbs around 15%-20% of the total impinging sunlight while the active layer absorbs only approximately 50%.

Prediction and tailoring of steady-state broadband sound fields in enclosures using absorption scaling and energy-intensity boundary elements.

Enclosures with diffuse reflection boundaries are modeled with an energy-intensity boundary element method using uncorrelated broadband directional sources. An absorption-based perturbation analysis shows the spatial variation of acoustic field obeys certain scaling laws. A series expansion in terms of average absorption gives separate boundary integral problems at each order. The lowest-order solution has a uniform level proportional to the reciprocal of the average absorption. The next-order solution is independent of average absorption and primarily responsible for spatial variation of the acoustic field. This solution depends on the spatial distribution of absorption and input power sources, but not their overall level. For the primary spatial variation, the effects of the relative distributions of absorption and input power are linear and uncoupled. These distributions can be expressed in terms of constituent spatial modes corresponding to the ways absorption and input power can be distributed. Solved numerically once for each mode, the acoustic field can be expressed in terms of the modal amplitudes in closed form. These amplitudes can be adjusted to tailor the spatial variation. Examples include how to distribute absorption to minimize sound levels in one location, or how to achieve a uniform interior field. [Sponsor: NSF.]

Prediction and tailoring of steady‐state broadband sound fields in enclosures using absorption scaling and energy‐intensity boundary elements

Enclosures with diffuse reflection boundaries are modeled with an energy‐intensity boundary element method using uncorrelated broadband directional sources. An absorption‐based perturbation analysis shows the spatial variation of the acoustic field obeys certain scaling laws. A series expansion in terms of average absorption gives separate boundary integral problems at each order. The lowest‐order solution has a uniform level proportional to the reciprocal of the average absorption. The next‐order solution is independent of average absorption and primarily responsible for spatial variation of the acoustic field. This solution depends on the spatial distribution of absorption and input power sources, but not their overall level. For the primary spatial variation, the effects of the relative distributions of absorption and input power are linear and uncoupled. These distributions can be expressed in terms of constituent spatial modes corresponding to the ways absorption and input power can be distributed. Solved numerically once for each mode, the acoustic field can be expressed in terms of the modal amplitudes in closed form. These amplitudes can be adjusted to tailor the spatial variation. Examples include how to distribute absorption to minimize sound levels in one location, or how to achieve a uniform interior field. (Sponsor: NSF)

Boundary element prediction of steady-state broadband interior sound fields using absorption-based scaling

Energy-intensity boundary elements are used in combination with the method of absorption-based scaling to predict steady-state broadband sound fields in enclosures with diffuse reflection boundaries. The wall absorption is expressed in terms of an overall absorption parameter—the spatially averaged value—and spatial variations around this mean. Boundary element strengths are expressed in a power series of the overall absorption, treated as a small parameter, thereby giving a separate problem at each order. The first problem has a uniform mean-square pressure proportional to the reciprocal of the absorption parameter. The second problem gives mean-square pressure and intensity distributions that are independent of the absorption parameter and are primarily responsible for the spatial variation of the reverberant field. This problem depends on the location of sources and the spatial distribution of absorption, but not overall absorption. Higher order problems proceed in powers of the absorption parameter, as corrections to the primary spatial variation. Boundary element solutions are obtained for each order, and the simplest model for spatial variation gives fairly accurate predictions. The method gives physical understanding of the causes of the spatial variation of enclosure sound fields and provides specific insights into the behavior and design of acoustic spaces.

Absorption-based scaling method to predict steady-state broadband sound fields in enclosures

An absorption-based analysis method is developed for steady-state broadband sound fields in enclosures having diffuse or specular reflection boundaries. The wall absorption is expressed as an overall spatially averaged value, with spatial variations around this mean. Interior pressures and intensities are expressed in a power series of the overall absorption, treated as a small parameter, thereby giving a separate problem at each order. The first problem has a uniform mean-square pressure level proportional to the reciprocal of the absorption parameter, as expected. The second problem gives a mean-square pressure and intensity distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the reverberant field. This problem depends on the location of sources and the spatial distribution of absorption, but not absorption level. Higher-order problems proceed at powers of the absorption parameter, but are essentially small corrections to the primary spatial variation. The primary spatial variation problem is solved using two different methods. Although formally developed based on treating absorption as a small parameter, the method is demonstrated to work remarkably well in practice up to large absorptions, and to provide insight into the behavior and design of acoustic spaces.

Analysis of temporal decay of diffuse broadband sound fields in enclosures by decomposition in powers of an absorption parameter

An analysis method for time-dependent broadband diffuse sound fields in enclosures is described. Beginning with a formulation utilizing time-dependent broadband intensity boundary sources, the strength of these wall sources is expanded in a series in powers of an absorption parameter, thereby giving a separate boundary integral problem for each power. The temporal behavior is characterized by a Taylor expansion in the delay time for a source to influence an evaluation point. The lowest-order problem has a uniform interior field proportional to the reciprocal of the absorption parameter, as expected, and exhibits relatively slow exponential decay. The next-order problem gives a mean-square pressure distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the reverberant field. This problem, which is driven by input sources and the lowest-order reverberant field, depends on source location and the spatial distribution of absorption. Additional problems proceed at integer powers of the absorption parameter, but are essentially higher-order corrections to the spatial variation. Temporal behavior is expressed in terms of an eigenvalue problem, with boundary source strength distributions expressed as eigenmodes. Solutions exhibit rapid short-time spatial redistribution followed by long-time decay of a predominant spatial mode.

Analysis of diffuse broadband sound fields in enclosures by decomposition in powers of an absorption parameter

A novel analysis for steady-state or time-dependent broadband diffuse sound fields in enclosures is developed. Beginning with a formulation utilizing broadband intensity boundary sources, the strength of these wall sources is expanded in a series in powers of an absorption parameter, thereby giving a separate boundary integral problem for each power. The first problem has a uniform interior field level proportional to the reciprocal of the absorption parameter, as expected. The second problem gives a mean-square pressure distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the reverberant field. This problem depends on the location of sources and the spatial distribution of absorption, but not absorption level. Additional problems proceed at integer powers of the absorption parameter, but are essentially higher order corrections to the spatial variation. The important second problem and the higher order problems are easily solved numerically, but closed form approximate solutions based on one iteration step are simple and accurate. Solutions obtained by retaining only the first couple of terms in the series expansion are compared to complete solutions obtained by another approach, and good agreement is shown between the two methods.

Sensitivity of room acoustic parameters to changes in scattering coefficients

This project uses the room acoustics computer modeling program, ODEON, to investigate the sensitivity of room acoustic parameters to changes in scattering coefficients. Particularly, the study is interested in determining if the results from certain room models are more sensitive to scattering coefficients than from other models, due to their geometry or absorption characteristics. If so, how can one quantify a model’s susceptibility to being sensitive to scattering? Various models of three real spaces in Omaha, Nebraska are tested. The predicted reverberation, clarity, and spaciousness parameters are compared at various receiver locations, while the scattering coefficient of all surfaces is varied from 0 to 0.1, 0.3, 0.5, and 0.8. The resulting data are analyzed by frequency according to the (1) average absorption of the room; (2) magnitude variation of absorption within the room; (3) spatial distribution of absorption within the room; and (4) level of model detail. Initial results indicate that parameters studied may show more sensitivity to scattering coefficients in models that have a wider range of absorption values, more disparate distribution of absorption, and lower detail level. Various schemes that include these aspects are proposed for computing a model’s sensitivity to changes in scattering.