Method and apparatus for thin layer monitoring

摘要

An apparatus and a method are provided for measuring the thickness (d) of a thin layer (12) of a non-metallic material on the surface of another medium (14). A transmitter (16) causes a beam of microwaves to be incident on the exposed surface (15) at an angle of incidence greater than 30 DEG , and at least one fixed detector (18) monitors a component of the reflected microwave beam polarized in an appropriate plane. In one case the angle of incidence is equal to the Brewster angle (B) for the lower medium, which is water, and the detector monitors the amplitude of the vertically plane polarized component, which is a rapidly varying function of the thickness. In another case the angle of incidence is about 45 DEG , and the monitored component is cross-polarized relative to the incident beam. The apparatus is suitable for detecting layers less than 1 mm thick of pollutants such as oil or kerosene on water before such water is discharged into the environment.