Biaxial Stretching Device for Stretchable Electronics

Stretchable electronics is a relatively new field in electronics. It has been researched quite intensively in the past 20 years, and significant progress has been made throughout the years. Interesting applications arise as the fabrication methods are developed further, and the most significant applications seem to lie in the medical and wearable field as well as robotics and sensor applications. The biggest advantage of stretchable electronics versus the traditional printed circuit board approach is that devices can be made to be less obtrusive, lighter, less noticeable and more comfortable. To this day, the testing of stretchable electronics is still far less standardized and organized than the rigid counterpart. The aim of this thesis is to develop a device to biaxially deform stretchable samples that are used mostly in on-skin and textile integration applications. The introduction of printing as a manufacturing method has boosted the interest in stretchable electronics, and the need for tests that emulate the real-life situations well enough is growing. The biggest interest lies in different types of biaxial deformation, symmetrical and asymmetrical. In real-life applications, the stretching of on-skin and textile-integrated stretchable electronics, for example, plaster-like health monitoring patches, is rarely symmetrical, which is why a testing method to better emulate real-life conditions is necessary. In addition to the biaxial deformation, the electrical properties of the samples are recorded simultaneously. It was found that biaxial testing methods for stretchable electronics have been rarely developed in the past, however, some examples can be found along with a readily available reference design. The benchmark device was built and characterized with digital image correlation (DIC) measurements. After the characterization, the weak points of it were identified, and a new design was introduced. The new device was characterized the same way as the reference device in order to obtain valid, comparable results. Lastly, a demonstration of simultaneous deformation and electrical measurement is done to show the behavior of example samples under stress. The development of the new device for testing stretchable samples was successful. The imposed strain on the samples was uniform and symmetrical, more so than in the case of the reference device. The design process of the device succeeded. In addition to outperforming the reference device, the new features introduced in the improved design are the most significant advantages. The new device is capable of imposing various different loading conditions on the samples, making it more useful in emulating real-life situations. However, some improvements for the future need to be done in order to maximize the potential of it. The asymmetrical biaxial mode needs to be further examined to identify the weak points of it. Also, the sample attachment system needs to be considered for redesign, as well as the attachment of the measurement probes. With the improvements, the built device will be able to better meet the requirements for precise, predictable functionality