Materials

1. Materials

2. What Are Materials? • All InSite features are ultimately composed of planar facets (or faces) which define the “geometry” • The set of material properties assigned to each facet determine its electromagnetic behavior for reflection, transmission, and diffraction • A foliage material is assigned at the structure level of foliage features in addition to the face level • A material’s properties also includes the display properties - color and, in some cases, thickness

3. Material Properties of Buildings and Terrain • Material properties are used to determine reflection, transmission and diffraction coefficients in ray-based propagation models • Each face is assigned a material • Predefined materials, such as concrete, wood, etc., are available • New materials can be stored in a modifiable database accessible to all projects

4. Material Types: Buildings and Terrain • Dielectric half-space • Layered dielectric • One or more lossy dielectric layers of finite thickness • PEC backed layer • Single lossy dielectric layer on top of a metal layer • Constant coefficient • Polarization dependent, independent of incidence angle • Perfect electrical conductor (PEC) • Free space • User-defined files • Magnitude and phase vs. incidence angle and polarization • Dependence on frequency and incident plane (optional)

5. Foliage Material Types • Complex Permittivity • Real and imaginary parts of effective permittivity • Lossy Dielectric • Real part of permittivity and conductivity • Attenuation • Attenuation in dB/m and real part of permittivity • Biophysical Properties • The effective permittivity is determined from the biophysical characteristics of the tree, such as leaf area, leaf density, branch size, branch density, etc. • Option for adjusting the effective permittivity to agree with a measured attenuation at a single frequency

6. Viewing and Editing Material Properties • Summary of materials can be viewed in main window • Right-click on a material to view/edit properties or plot • Also select materials from Project Hierarchy window • Materials database can be viewed by clicking on bar at the bottom of the window

7. Material Properties Windows • Each material type has its own properties window • The “layered dielectric” is one of the more versatile material types • Roughness is only applied to the outer surface of the first layer • Double sided faces will use the same material, and the same order of layers for both sides

8. User-Defined Coefficient Files • Separate files for reflection and transmission coefficients • Files contain magnitude, phase vs. incidence angle for parallel and perpendicular polarization • Several data format options are available • File format allows for multiple frequency records • Also an option for coefficients which vary with orientation of the incident plane • Option for cross-polarized coefficients will be added in a later version

9. Materials Database • At installation, the materials database includes a small number of common building, ground and foliage materials • Database can be viewed from the materials section of the main window • Materials in database are available to all projects • New materials can be added and existing ones modified • Note: Once a database material is assigned to a feature it becomes part of that feature and any association with the entry in the database is lost. Changes made to the feature’s material are not applied to the material in the database, and vice versa.

10. Data Sources for Dielectric Properties • User’s manual has a list of references for dielectric properties of buildings, terrain, and foliage materials • Reflection and transmission coefficients at normal incidence appear to be measured more frequently than the permittivity and conductivity of the material • No good models for frequency dependence of permittivity of most building materials at present, so measurements at a different frequency than the one of interest should be used with caution • Models are available for frequency dependence of ground dielectric parameters and foliage (< 1 GHz)

11. Dielectric Properties of High-Rise Buildings • Effective relative permittivity is usually between 4 and 9, with 5-7 being the typical range. The effective conductivity is usually between 1x10-4 and 1x10-2 S/m • Building surfaces are usually not homogeneous, so the permittivity is, in some sense, an average over the surface • Permittivity is one of the few adjustable parameters when path loss measurements are available • Propagation by multiple reflection (with or without diffraction) amplifies effect of building permittivity. After 6 reflections the path loss for a permittivity of 4 can be 20 dB higher than for a permittivity of 9, assuming reflections are all near normal incidence. Grazing incidence will give a lower difference.

12. Biophysical Foliage Material • Foliage is modeled as a collection of randomly oriented scatterers (the leaves and branches) • Bio-Physical Inputs: Size of scatterers, orientations, density, dielectric properties of branches and leaves • Yields an effective permittivity for the foliage which is frequency and polarization dependent

13. Use Attenuation Measurements to Adjust Biophysical Parameters

14. Use Attenuation Measurements to Adjust Biophysical Parameters (2) • Attenuation measurements available for a large number of tree types at UHF • Vogel, W., Goldhirsh, J., “Tree attenuation at 869 MHz derived from remotely piloted aircraft measurements”, IEEE Transactions on Antennas and Propagation, Vol. 34 Issue 12 , pp. 1460 –1464, Dec. 1986 • Goldhirsh, J., Vogel, W., “Roadside tree attenuation measurements at UHF for land mobile satellite systems,” IEEE Transactions on Antennas and Propagation, Vol. 35 Issue 5, pp. 589-596, May 1987 • J. Goldhirsh, W. J. Vogel, “Handbook of Propagation Effects forVehicular and Personal Mobile Satellite Systems,Overview of Experimental and Modeling Results”, NASA Reference Publication 1274, 1992 • Estimate seasonal variation in effective permittivity • Physics-based model allows for frequency scaling

15. Reflection and Transmission Coefficients • Plot coefficients vs. incidence angle or frequency • Other options include: magnitude, phase and polarization • Use export and import options to get multiple plots on a graph

16. Reflection Coefficients for Rough Surfaces • Surface roughness reduces specular reflection • Rough surface coefficient is determined by multiplying the smooth surface coefficient R0 by a factor which depends on angle of incidence, wavelength and RMS variation (Δh) in surface height about mean level • Multiplying factor is smallest at normal incidence and approaches 1 at grazing incidence • This correction assumes a Gaussian rough surface • No diffuse scattering is included in Wireless InSite at present

17. Summary • A variety of material types are available • Dielectric layers, dielectric half-space, user-defined, etc. • Material properties are used to determine reflection, transmission and diffraction coefficients • Coefficients can be angle, frequency and polarization dependent • Foliage material properties determine attenuation and refraction of lateral wave • Materials can be added to a database which is shared among all projects