7 - Radar technology: radio frequency, interferometric, millimeter wave and terahertz sensors for assessing and monitoring civil infrastructures

Abstract

Radar and millimeter wave methods provide a means of remote and noncontacting examination of structures through controlled electromagnetic (EM) interactions. Metallic and nonmetallic structures reflect and scatter EM waves impinging at the outer surfaces. Nonmetallic, i.e., dielectric, materials allow for EM waves to penetrate the surface, and scatter or reflect off of subsurface objects and features. Actively measuring surface and subsurface reflectivity and scattering by the controlled launching and receiving of EM waves provides information that when suitably processed can indicate surface and subsurface feature geometry, material properties, and overall structural condition. These active EM technical tests are often called “Ground-Penetrating Radar” for EM wave frequencies less than about 10GHz and “Millimeter Wave” methods for those at higher frequencies. This chapter describes the range of uses, operating principles, signal processing, and data interpretation for these methods.