3-D Printed Inductive Displacement/Force Sensor

This article presents a flexible inductive sensor fabricated using additive 3-D printing technology. The sensor is designed in the form of a double-spiral structure and consists of two parts: the body and the lid. The designed parts of the sensor were made of a polylactic acid (PLA) filament. Inside the body, a conductive wire is embedded. The structure is thin enough to be elastic and, therefore, it is suitable for displacement or force measurement. The structure can be easily extended, which causes the inductive coupling between the spiral traces to decrease, lowering in turn its self-inductance. When it is used as a sensor, self-inductance serves as the measure of displacement. Displacement measurements up to 26 mm with 2 mm steps were made using the
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meter HP4227A. Three sensor structures with an outer dimension of 4.5 cm and a varying number of spiral turns (3/4, 5/4, and 7/4) were produced and examined. The change in inductance with displacement for all three structures was modeled and analyzed. The numerical simulation was compared with the obtained experimental results, and good agreement was found (the difference is below 10%). The measurement results confirmed the efficiency of the designed sensor. Additionally, measuring respiratory rate is proposed as one of its potential applications in medicine.