This paper introduces the design and analysis of a small-size coaxial resonant applicator for high-speed microwave heating assisted additive manufacturing of multiple materials, such as continuous carbon fiber reinforced polymer composites, thermoplastic and metal parts. The elaborated coaxial resonant applicator reduced the size and has a resonant frequency between 2.4 to 2.5 GHz. A TEM wave is stimulated in the applicator where the electrical field is polarized perpendicular to the filaments and therefore allows a maximum penetration depth. The electrical conductive filament is designed as part of the inner conductor to enhance coupling efficiency. To prevent microwave leakage induced by the conductive material, a compact quarter wavelength filter was developed. The equivalent circuit of the filter was used to analyze the influence of structural parameters on the resonance frequency. The filter has been tested and good agreement between measured and simulated results is obtained. The heating behaviour with varying input power has been investigated for polyamide, polylactic acid and continuous carbon fiber reinforced polyamide filaments.

Carbon-fiber-reinforced plastics (CFRPs) are of increasing popularity in a wide range of applications, and microwave curing promises significant reduction in processing times. However, for the design of an efficient microwave curing system, the composites’ effective material parameters must be known. This work presents a measurement system using a wall perturbation approach with a coaxial cavity to determine the effective conductivity of a CFRP along the fiber direction.