Nondestructive Microwave Thickness Measurements of Dielectric Slabs

Nondestructive evaluation of material using microwaves is receiving more attention because microwaves are capable of penetrating into lossless material; other characteristics, such as detecting reflections from boundaries, phase detection, etc., make microwaves very attractive for certain applications. This paper discusses two techniques (transmission and reflection) for measuring thickness of dielectric slabs and slabs backed by conducting plates. Theoretical and experimental aspects of each technique are outlined in detail along with limitations associated with them. Thickness of plexiglass and synthetic rubber slabs are measured with very good accuracy. The transmission technique is capable also of determining dielectric permittivity of a slab whose thickness is known, making the technique a versatile one