Preliminary Study on a Strain Sensor Printed on 3D-plastic Surfaces for Smart Devices

Nowadays, the increasing demand to realize plastic objects and devices equipped with sensors and electronics in the field of Internet of Things (IoT) and Industry 4.0 has required new fabrication methods. The best approach is to realize the sensors directly onto the object surface, which is usually 3-dimensional (3D) or non-planar. In this way, sensors and electronics could be perfectly integrated with the objects, avoiding the use of adhesive materials. The printed electronics represents a viable solution for producing smart devices in term of costs, variety of functional materials, throughput and reliability. Among the different printing methods, the aerosol jet printing (AJP) allows producing electronics and sensors directly onto non-planar and 3D surfaces. The photonic sintering cures the deposited metallic films, reducing the process time and avoiding the overheating of substrates characterized by low thermal stability. In this way, combining with photonic sintering, the AJP can be adopted for a wide variety of substrates, like paper, plastic, fabric and tissue. In this work, a first example of strain gauge printed directly on a PVC tube with the AJP and treated with photonic sintering is presented. The silver-based sensor was designed, realized and characterized. The thickness of the silver film (8 μm in average) was measured with a profilometer. The tube was bent in a cantilever configuration up to 0.5%. The relationship between mechanical deformation and electrical resistance is linear, with a gauge factor of 1.04. The decay over time of the resistance change under constant strain is about 0.05%. The proposed method is a promising fabrication solution for smart devices in IoT and Industry 4.0 applications.