Industrial applications of noncontact ultrasonics techniques

In many application environments, it is not possible to practice nondestructive evaluation (NDE) by physically contacting the material under test with probes. Examples include the evaluation of objects that are moving (e.g., on an assembly line), hot materials, materials that cannot risk contamination, and more. Lack of contact means that, typically, the coupling material is air. This poses specific requirements, due to the acoustic impedance mismatch that an air layer can provoke and the consequent energy losses. In this chapter, some examples of setups, transducer arrangements, and signal processing strategies capable of addressing such requirements are illustrated, showing how concepts presented in the previous chapters can be deployed in this particular context. Furthermore, some typical achievable results are illustrated, with respect to a few different testing scenarios, such as the testing of composite materials, the inspection of concrete, imaging of surfaces or thin materials, and food inspection.