arealdichte

Arealdichte, or areal density, is a measure of a quantity distributed over a two-dimensional area. It expresses how much of something exists per unit area and is defined as Sigma_A = Q / A, where Q is the total quantity and A is the surface area over which it is spread. The unit depends on what Q represents; for example, mass per area is measured in kg/m^2, while the number of particles per area is counted in particles/m^2 or similar.

In the context of thin films and coatings, areal density relates to the film’s volumetric density and thickness. For a homogeneous material, Sigma_A = rho * t, where rho is the material’s density and t is its thickness. This also allows thickness to be inferred when density and areal density are known (t = Sigma_A / rho).

Applications of arealdichte are diverse. In materials science and engineering, it is used to characterize coatings, films, and deposited layers. In environmental science and ecology, biomass, leaf area, or vegetation cover can be described as areal density (for example, g/m^2). In astronomy and geophysics, densities of stars, particles, or other objects are often expressed per unit area or per unit solid angle.

Measurement methods include high-precision weighing of a sample with a known area, optical or interferometric techniques to determine thickness and density, and remote sensing or image analysis for spatially distributed quantities.

Limitations include the assumption of a well-defined, uniform area and distribution; many real-world situations are heterogeneous, requiring averaging or spatially resolved measurements.