A system to measure the complex permittivity of 3D-printing materials

Additive manufacturing has brought a technological revolution which up to now has shown only glimpses of the future developments made possible. Besides human ingenuity, an important component of the development process is the accurate knowledge of the 3D printing materials properties. In high frequency applications, the complex permittivity of dielectric materials is the fundamental quantity needed for the proper design and for the optimization of innovative sensors. The versatility of 3D printing allows for many shapes, sizes, combination of electrical properties. Moreover, high frequency (microwave) applications span operating frequency ranges from below 1 GHz to several tens of GHz. Hence, many measurements techniques for the determination of the complex permittivity have been developed, with various accuracies and addressing specific scenarios. In this work we propose two resonators: a dielectric loaded one, operating at higher frequency 12.9 GHz, capable of measuring thick > 1 mm flat dielectric samples, eventually with backing metal as encountered in microwave circuits; and a split ring resonator, working at 2.2 GHz, for the measurement of thicker samples, possibly in in-field scenarios. To demonstrate their measurement capabilities we have tested 3D printed samples with different fillings in order to expand the range of complex permittivity test values. The two resonators yield consistent results, providing a reciprocal validation, with similar accuracies competitive with other existing solutions.