Kirigami-Based Approaches to the Development of Highly Tunable Mechanical, Electrical, and Optical Systems and Devices

I use kirigami techniques to create high performance, 3-dimensional structures, mechanisms, and multi-functional devices with applications in wearable electronics, optomechanical systems, solar energy harvesting, and electromagnetic wave propagation. Kirigami refers to cutting or creating negative space in a material. This design technique is used to create sophisticated 3D structures and devices starting from flat sheets to achieve unprecedented capabilities and performance that would be difficult to achieve using conventional fabrication approaches. I first explore novel rotationally symmetric kirigami (RSK) structures and their mechanical properties using a combination of experiments, analytical, and finite element modeling. I also show and analyze how the cut pattern influences the structure’s cross-plane deformation, enabling the shape to assume globally curved surface contours without wrinkling or buckling the material. This analysis enables a number of different applications, which are discussed below. I then study the stress and strain distribution across the kirigami structure conforming to a curved surface envelope, where the localization of stress at the saddle-points in the kirigami structure relates to the degree of curvature upon deformation. Rigid electronic components can be integrated with the shape in its flat state without stressing the components upon deformation, making it compatible with mass-manufacturing processes. I also show how other components – i.e., strain gauges – can be placed in regions of substantial strain to measure small deformations. These effects are leveraged to create an inexpensive wearable sensor platform that conforms to the shoulder joint to monitor complex motion and muscle behavior, which are notoriously challenging to track. This may help facilitate rehabilitation, athletic training, feedback control for augmented mobility, robotics, and other applications. Using the concept of a closed shape and rotational symmetry of cuts, I demonstrate a multi-axis optical tracking system. Here, out-of-plane deformation and linear translation induces simultaneous tilting of a subset of beams enabling its use as a tracking mechanism. One application of this mechanism is for daily and seasonal tracking of the sun, which I demonstrate by integrating thermoformed concentrators and high efficiency photovoltaic cells with the kirigami structure. Over 110° tracking range and an 80x concentration factor can be achieved while maintaining the height of the tracking array to less than 4 cm. The array is actuated by a finite (e.g., 2.5 cm) lateral displacement irrespective of array size. This work potentially opens the path to substantially lowering the cost of electricity from photovoltaic panels in space-limited areas. In addition, I explore the use of other materials in kirigami structures to achieve emergent properties for other applications. The use of polymer composites to enhance the absorption of electromagnetic waves for EMI shielding is demonstrated. Other examples include shape memory alloys and polymers to enable reconfigurable structures for aerospace, automotive, medical, robotics, or flexible electronic applications, as well as a dynamic 3D platform designed to promote cardiomyocyte maturation.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/167953/1/evkee_1.pd