LSU: Thesis Student 3D Prints Strain Sensors for Electronics & Wearables

Louisiana State University thesis student, Austin Smith, hits the mark in exploring mechanisms for sensors in wearable electronics. In ‘Design and Fabrication of FDM 3D Printed Strain Sensors,’ the author explains that there is much more demand today for affordable sensors that can be created quickly due to the availability of flexible electronics requiring monitoring of movement.

Most strain sensor research has been focused on sensitivity, elasticity, and actual fabrication. Here, Smith sought to develop a way to integrate more than one sensor into a single device, using materials and techniques offering the capability for strength and performance. Samples of two different sizes: Type I at 2000 μm by 200 μm and Type II at 500 μm by 200 μm, allowed Smith a better chance to examine and evaluate the prototypes.

Representative Diagram of Embedded 3D printing based on Muth et al. procedure

Once created, each sensor consisted of:

• Embedded channels (both long and short)
• Conducting fluid
• Substrate

“When an external force was applied, the channels deformed, and the cross-sectional area of the long channels reduced while the cross-sectional area of the short channels increased. As a result, the deformation of the long channels caused a reduction in the cross-sectional area of the conducting fluid. This change in area of the conducting fluid reduced the size of the path the current could flow through and thereby, increased its resistance,” stated Smith.

Cross-sectional view of the 3D printed strain sensor design.

Working principle of the channel effects when under applied strained.

Galinstan fluid was used for the research project because of conductivity and relative lack of toxicity, with Smith noting that the strain sensor pattern was suitable for single axis strain. An Ultimaker 3 3D printer was used to print the sensors, fabricated with Ninja Flex Thermoplastic Polyurethane. Overall, the research showed that a range of complex designs and sensor platforms can be created via FDM 3D printing.

Setting and parameters used to print the strain sensors using Ultimaker 3 3D printer.

“Nonetheless, issues related to strain offset, stress accumulation, and stress concentration were limiting factors. The way the FDM process formed the elastic substrates was such that the fibers were interwoven and at an angle with respect to the applied strain,” concluded the author. “This reduced the strain required to cause permanent deformation and strain accumulation in these fibers.

“These observations were highly relevant to the creation of 3D printed strain sensors as the patterning of the layers could alter the strain response of the strain sensor. Overall, FDM 3D printing has been shown to have potential as a method of simple and cost-effective fabrication of flexible strain sensors.”

As 3D printing and electronics continue to accompany one another in countless innovations today, sensors are a popular focus also for many different applications, from embedded components to biomedical sensors to fiber optics. Find out more about strain sensors in electronics like wearables here. What do you think of this 3D printing news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.