Applications

During the past 3+ decades, microwave NDE techniques have been steadily employed for an increasing number of applications. There are several key reasons for this, namely:

• rapid increase in commercial availability of affordable, off-the-shelf and increasingly capable microwave and millimeter wave components, devices and measurement systems that are at the core of microwave and millimeter wave NDE inspection system design,
• sustained development of specific testing and evaluation methodologies that are applicable to a specific or a diverse set of NDE applications,
• availability of a host of capable and robust numerical electromagnetic simulators and solvers that are capable of full-wave modeling of the interaction of these waves with complex structures, 
• development of applications-dedicated software packages, and 
• the ever-increasing utility of composite materials and structures demanding NDE methods that offer capabilities that overcome certain limitations associated with standard NDE methods.

The following is the list specific applications to which microwave NDE methods can be successfully applied:

• Materials Characterization:
  • Materials characterization using wideband complex permittivity and permeability assessment of materials.
  • Correlating permittivity and permeability information to physical, chemical and mechanical properties of materials. For example: 
    • porosity estimation in composites and ceramics (e.g., thermal barrier coatings (TBC))
    • cure-sate monitoring of chemically-reactive materials
  • Inspection of layered composite structures, including:
    • evaluation of coating thickness and materials properties for materials such as paint, primer, ceramics, etc.
    • detecting and estimating thickness (i.e., severity) of corrosion under paint and other laminate coatings
    • detection of disbonds, delaminations, and voids in layered and thick composite structures
    • inspection of aircraft radomes
  • Evaluation of cementitious materials, specifically:
    • assessing water-to-cement ratio (w/c) in fresh and hardened cement paste, mortar and concrete,
    • evaluating material properties of concrete including aggregate volume content, distribution and size, 
    • detection of grout-filled cells in masonry bricks,
    • detection and evaluation of chloride permeation in concrete, 
    • detection and evaluation of alkali-silica reaction (ASR) gel in concrete,
    • detection and sizing of delamination between FRP composites and cement-based materials such as CFRP-strengthened concrete bridge members
  • Characterization of surface conductivity of conductive materials.
  • Crack Detection and Characterization: 
    • Detecting and sizing surface-breaking fatigue cracks in metals, when exposed or masked under a dielectric coating (e.g., paint).
    • Detecting other metal surface anomalies (e.g., surface roughness, surface manufacturing flaws in rolled metal products).
  • Chipless RFID:
    
    • Chipless RFID tag design for identification and materials characterization applications.
  • Imaging:
    • High-resolution near-field methods.
    • Lens-focused high-resolution method.
    • Real-time synthetic aperture radar (SAR) and holographical or 3-D techniques.
    • Imaging steel, glass-fiber reinforced polymer (GFRP), carbon-fiber reinforced polymer (CFRP), and basalt reinforcing bars in concrete.
  • Other:
    • Hybrid measurement techniques using embedded modulated scattering PIN diode-loaded dipole antennas for material characterization and microwave imaging.
    • Noninvasive diagnosis of human skin for cancers and burns. 
    • Active microwave thermography.
    • New applications being discovered