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Single-process 3D printing of sensors

Figure: Sensing of finger joint rotations using piezoresistive sensor elements. Image author: Luka Frančič

Publish Date: 03.01.2022

Category: Our contribution to sustainable development goals

Sustainable development goals: 3 Good health and well-being, 9 Industry, innovation and infrastructure (Indicators)

An innovation by researchers from the Faculty of Mechanical Engineering, University of Ljubljana, will enable the printing of custom-made prostheses and surgical aids.

The conventional manufacturing of polymeric piezoelectric sensors consists of roughly three steps. In the first, a piezoelectric film needs to be made, which generates a charge when under an applied stress. In the second step, conductive electrodes are applied in the direction of the thickness, with which the generated charge can be measured. In the third step, a high electric field is fed to the electrodes in the polarization process at elevated temperature – this electric field aligns the molecules in the piezoelectric layer, thus increasing the sensor’s sensitivity. Conventional multi-stage manufacturing usually limits the complexity of the shape of the sensors and consequently restricts their applicability in cases in which measurements need to be done in difficult to reach places, or when sensor elements already need to be installed during the manufacturing phase of the product to be produced.

Piezoelectric sensors convert mechanical energy into electric energy. Upon stress or deformation, an electric charge is created, which can be measured. Sensors are thus used to control the state of a structure – to measure dynamic stresses, deformations and lifetime.

In an article published in the high-impact factor (10.998) journal Additive Manufacturing, two researchers from the Laboratory for Dynamics of Machines and Structures at the Faculty of Mechanical Engineering, University of Ljubljana, namely young researcher Tilen Košir and Prof. Janko Slavič, PhD, managed to combine all three of the above-mentioned steps of manufacturing piezoelectric sensors in a single process with the help of 3D printing (more precisely, the method of targeted material application called fused filament fabrication).

Using commercially available materials, a piezoelectric layer was 3D printed in a single process, along with conductive electrodes which were then automatically connected to the source of high voltage during the manufacturing process. Consequently, the process of sensor polarisation could already be done during the phase of 3D printing. The presented principles enable the manufacturing of piezoelectric sensors of any shape, and among other things also allow the installation of such sensors in other functional 3D printed products in a single process, even in places which are usually inaccessible. In medicine, they can be used in the field of custom-made prostheses or surgical aids.

FS 3D tisk 1

The figure presents the concept of 3D printed piezoelectric sensors and the polarisation process. Source

FS 3D tisk 2

The figure presents a case of printed piezoelectric sensors: a) view from above, b) view from below. Source

The project was partially financed as part of the Mechanics in Technology programme group (ARRS, P2-0263), and a research project entitled Single-process 3D printing of dynamic sensors (ARRS J2-3045, 2021-2024).

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