Kirigami patterns stretch the abilities of piezoelectric films

Despite the countless applications that utilize piezoelectric materials, the human body still poses numerous challenges to their use in biomedical and implantable devices. To tackle the key issue of stretchability imposed by human tissue’s highly deformable nature, researchers developed a piezoelectric strain sensor using the paper cutting patterns of kirigami. As described in Applied Physics Letters, the piezoelectric sensor is highly stretchable and produces high voltage outputs, both desirable features for biomedical use.

Inspired by previous work developing metamaterials with unusual deformation characteristics, researchers cut patterned slits into 2-D films of flexible polyvinyl fluoride. Their algorithmically designed patterns provided the piezoelectric films with mechanical pliability. To produce a specific mechanical performance, a given pattern design took into account millimeter-scale dimensions like cut lengths and spacing as well as the higher order dynamic effects of the substrate, which were tens to hundreds of micrometers in thickness, such as buckling.

“Cuts and slits into a real 2-D substrate generate some very interesting out-of-plane deformations, which include buckling and flapping of the edges,” said Fabrizio Scarpa, one of the authors. “These out-of-plane rotations of the film actually trigger different global mechanical and electric responses in the sensor.” A proper kirigami architecture, he noted, takes advantage of these structural effects as features, rather than simply trying to avoid them.

With the help of finite element analysis, they also optimized the positioning of topological electrodes on segments of the film to avoid charge cancellation that would reduce the voltage output. Compared to continuous electrodes used more commonly, these devices demonstrated 2.6 times higher voltage performance.

According to Scarpa, they are already testing the device over soft, curved materials to optimize performance. The group is also looking at potential design improvements, such as reducing the spacing between cuts and using more advanced electrode patterning techniques.

Source: “Kirigami stretchable strain sensors with enhanced piezoelectricity induced by topological electrodes,” by Rujie Sun, Bing Zhang, Lu Yang, Wenjiao Zhang, Ian Farrow, Fabrizio Scarpa, and Jonathan Rossiter, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5025025 .