Control of Additive Manufacturing for Radio Frequency Devices With Spatially Varying Dielectric Properties

Additive manufacturing (AM) is increasingly being used to fabricate end-use and high-value-added parts in a range of industries. AM's ability to create complex geometries and vary the internal composition of a part has enabled the design of many novel devices, including radio frequency (RF) devices that rely on the spatial variation of electromagnetic (EM) properties. However, current AM processes for fabricating complex parts are typically run without any part monitoring or online feedback control, and as a result, the printed parts may be compromised by defects or have poor tolerances. Manufacturing parts in this way also requires extra quality testing since there is no knowledge of their interior quality. For these reasons, introducing process monitoring and corrective action to the AM process has become an important area of research as AM is being used to create safety-critical parts. This work proposes a control algorithm to enable closed-loop control of an EM property, specifically dielectric permittivity, within a print using a fused filament fabrication (FFF) printer. The control system used a split-ring resonator (SRR) to measure the permittivity of printed thermoplastic, and the control action was applied by updating the printed infill density layer to layer. This control system was tested by printing a proof-of-concept graded-index (GRIN) lens with spatially varying permittivity through the lens' length. The results demonstrate the ability of the controller to follow a constantly varying reference signal, indicating the potential of closed-loop control for improved fabrication of functional RF devices that depend on precise variations in relative permittivity.