Determination of material properties like permittivity and density with microwaves

With the help of electromagnetic waves in deci-, centi- and millimeter-wave range (microwaves) it is possible to determine the properties of non-metallic objects like permittivity or density in a nondestructive and if necessary in a contactless way. Depending on the type of the test object the measurement can be carried out both with low-cost narrowband or more expensive wideband devices and sensors. To get the characteristic value in most cases it is necessary to calibrate the test device with the help of reference materials. It is recommendable to sustain a constant distance(lift-off or standoff) between the antenna of the sensor and the test object. The paper deals with the characterization of asphalt, especially the determination of its density.