Inductive proximity sensors within a ceramic package manufactured by material extrusion of binder-coated zirconia

Abstract

The embedding of electric components into additively manufactured structures offers enormous potential for extending the functionality and applications of parts produced by additive manufacturing (AM). However, the production of electric components embedded with 3D-printed ceramic structures has been a significant challenge due to the complexity of the manufacturing process and the high-temperature post-processing it requires. In the present study, an inductive proximity sensor with a 3D-printed ceramic housing and embedded sensing elements was designed and produced using a hybrid manufacturing process in which the printing process is paused and a sensing element is embedded into the printed structure. Sensing elements materials were carefully selected and intra-sensor structures were developed to ensure that the sensing element would survive in a high-temperature sintering environment. In the developed process, binder-coated zirconia containing 87 wt% was used as feedstock in a piston-based material extrusion process to fabricate the ceramic housing for the sensor, and platinum wire was used in the sensing element. The subsequent debinding and sintering processes achieved a nearly fully dense ceramic housing that protects the sensor in harsh environments. The successfully fabricated sensor was tested by measuring the change of distance between the inductive and metallic target and determining if the changes in distance would alter the inductance of the sensor. Results show that the sensing element maintains functionality throughout each fabrication step, and the fully packaged sensor also demonstrates the ability to work properly at high temperatures (in the range of 200–400 °C). At a frequency of 2 MHZ and a voltage of 1 V, the inductive sensor has a measurement range of approximately 7.0 mm. Additive manufacturing of the sensor housing enabled precise control of the geometry, dimensions, and infill density. Because the developed methodology allows for control of the type and structure of the sensing element, it can be used in the manufacture of a wide variety of sensors or smart components.