History of Microwave and Millimeter Wave Nondestructive Testing and Evaluation

The use of microwaves for nondestructive testing (NDT) dates back to the 1950s with some renewed interest in the 1960s. A resurgence of new R&D activities started in the 1990s and has continued since, expanding to include nondestructive evaluation (NDE) for quantitative measurement of materials. The term NDT&E is used to include both. There are several important reasons why these techniques have experienced continued increase in their utilities, namely:

  1. sustained level of technical maturity,
  2. availability of off-the-shelf devices, components and test equipment at microwave and millimeter wave frequency ranges,
  3. flourishing and every-increasing utility of non-metallic composite structures in a wide range of applications,
  4. limitations of other standard NDT techniques when addressing certain specific needs, and
  5. increased level of comfort in using “viable new” NDT&E techniques by practitioners.

Early on, microwave and now combined with millimeter wave techniques were considered as “emerging techniques”. However, as the utility of microwave and millimeter wave NDT&E techniques has increased, currently they are no longer considered as such. In 2016, the American Society for Nondestructive Testing (ASNT) formally recognized Microwave NDT as a separate method on its own.