3D printing of multi-material objects enables the design of complex 3D architectures such as printed electronics and devices. The ability to detect the composition of multi-material printed inks in real time is an enabling feature in a wide range of manufacturing sectors. In this study, dielectric properties of microscale embedded metal particles in a dielectric matrix have been characterized using impedance measurements as a function of particle size, shape, volume percentage and frequency. Measurements were found to agree well with calculations based on an anisotropic Maxwell-Garnett dielectric function model. Despite the metal loading exceeding the theoretical percolation threshold, a percolation transition was not observed in the experimental results. With this data, a calibration curve can be established to correlate metal loading with impedance or capacitance, which can be used with an in situ sensor for ink composition measurements during extrusion-based 3D printing. We demonstrate how an in situ sensor can locally measure the composition of the ink, allowing greater control over the resulting properties and functionality of printed materials.
Additive manufacturing offers new routes to lightweight optics inaccessible by conventional methods by providing a broader range of reconciled functionality, form factor, and cost. Predictive lattice design combined with the ability to 3D print complex structures allows for the creation of low-density metamaterials with high global and local stiffness and tunable response to static and dynamic loading. This capacity provides a path to fabrication of lightweight optical supports with tuned geometries and mechanical properties. Our approach involves the simulation and optimization of lightweight lattices for anticipated stresses due to polishing and mounting loads via adaptive mesh refinement. The designed lattices are 3D printed using large area projection microstereolithography (LAPuSL), coated with a metallic plating to improve mechanical properties, and bonded to a thin (1.25 mm) fused silica substrate. We demonstrate that this lightweight assembly can be polished to a desired flatness using convergent polishing, and subsequently treated with a reflective coating.
*This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 within the LDRD program. LLNL-ABS-738806.