Electromagnetic Signal Attenuation in Construction Materials
William C. Stone
Laboratory studies of electromagnetic (EM) signal propagation through construction materials were carried out as part of the NIST initiative in Non-Line-of-Sight surveying technology. From these data it is possible to determine several important material-specific characteristics needed for the design of engineering systems which make use of EM signal propagation through matter: 1) the power attenuation as a function of the material thickness and 2) the values of the electrical permittivity and dielectric constants for a particular material as a function of frequency. The latter can be used to calculate the propagation delay time associated with an EM pulse penetrating through a specified thickness of a given material. This information is essential for error compensation for time-of-flight metrology instrumentation systems. In this report, only the power attenuation aspects are discussed; dielectric and permittivity constants will be discussed in a future volume. The materials investigated included brick, masonry block, eight different concrete mixes, glass, plywood, lumber (spruce-pine-fir), drywall, reinforced concrete, steel reinforcing bar grids, variations of the plywood and lumber tests in which the specimens were soaked with water, and composite specimens involving brick-faced masonry block and brick-faced concrete. For each material, varying thickness specimens were fabricated in order to measure attenuation as a function of penetration distance. Each specimen was placed in a special test range consisting of spread spectrum transmission and reception horns spaced 2 meters apart with a metal RF isolation barrier located midway between the antennas to eliminate multipath signals. The isolation barrier contained a window at its center against which the specimens were fit. Measurements of power loss were taken at 2 MHz intervals from 0.5 to 2 GHz and from 3 to 8 GHz.