High-Resolution Millimeter-Wave Near-Field Evaluation of Additive Manufactured (AM) Polymeric Structures

Additive manufacturing (AM) is a rapidly growing industry whose utility has been expanded beyond metals and to other materials such as polymers, ceramics, and concrete, to name a few. However, advancement in the development of inspection techniques, particularly in-line nondestructive testing (NDT) methods, lags significantly. Most of the research in developing such methods has focused on metal-based AM. This paper presents a high-resolution dielectric-loaded waveguide probe for detecting small flaws in 3D printed polymeric structures. The electromagnetic (EM) design and optimization of such a probe are discussed in this paper. The probe design is based on concentrating the interrogating electric field of an open-ended waveguide in a thin dielectric slab insert. This results in obtaining a higher spatial resolution than when using only the open-ended waveguide. Subsequently, such a probe was fabricated at a frequency of 74 GHz (V-band (50-75 GHz)) and was used to raster scan a Thermoplastic Polyurethane (TPU) sample, with very small surface flaws, to generate a near-field image. The resulting image confirms the usefulness of this technique as a potentially viable method for in-line monitoring of polymeric AM structures.