Design and development of optical, optoelectronic and sensing systems for a luminous electronic tile

The work described in the dissertation is strictly related to LUMENTILE™, a project funded by the European commission in the framework of the Horizon 2020 research program. The final goal of the project was the development of a luminous electronic tile (hence the name) at a prototype level (TRL 7) offering a demonstration of the technologies used. Namely, large area electronics and integration of electronics and optoelectronics technologies with a non-standard material like ceramic. The project envisaged three different products. Two models were devoted to installation on floors and walls, working in a low speed regime in terms of colour displaying. The third model is thought for large video screen installations and for this reason able to work at high refresh frequencies regimes, in the order of 100Hz (high data rate, HDR tiles). The two low speed products (low data rate, LDR tiles) required the interaction with the user, and the installation is foreseen in public spaces where solicitations are frequent and the requirement in terms of resistance and durability are necessary for a device to be installed and used correctly. The main idea and the guiding principle of the project was to create an inconspicuous device. The final user should not realise to staring at an electronic device. On the contrary, LUMENTILE™ should be perceived as a usual decorative and passive element, coming to life only after a soft interaction. Not to distort the essence of a standard tile, while offering interactions and responses of a smart device; LUMENTILE™ was thought to resemble in shape and materials as a standard tile, embedding all the electronics required for its functioning. An interdisciplinary study across electronics, software, mechanical science and building engineer was needed to achieve the best possible level of integration. Among all the technologies and processes involved in the design and production of the full product, in this dissertation the focus will be on the optoelectronic and optical side. The topics in these aspects are related to: • Light source identification and design of a driving system • Design and development of an optical structure to offer uniform illumination of the tile surface • Design and implementation of an optical gesture recognition sensing system. The light source installed in LUMENTILE™ are standard high power semiconductor LED. Three of them, red, green and blue, are used in every individual light source to offer a large gamut of colour to the tile. A dedicated driving system was developed. The proposed design helped to highly reduce the number of components, the area occupation and the reduction of costs. A multiplexing in time of current is the basis to the proposed device, while the use of a PWM is offering the dimming and colour mixing feature. To obtain a good uniformity of the illumination on the tile surface, a light guide approach was proposed. The technology is known in the display field, where the requirements are though different from the ones of LUMENTILE™. The designed light guide is reconciling the mechanical properties required to this components, which needs to be structural; low complexity in the assembly phase, keeping at minimum the number of components and costs; and acceptable optical performances. The gesture sensing system, based on the concept of triangulation, allows to detect the movement of an object in front of the tile (a hand) and offers a touchless interaction with the device. The system is based on an infrared emitter which illuminates the space in front of the tile, where the hand will wave to require any action to the tile. A portion of the light scattered by the hand is then sent back to the tile and detected by four photodiodes placed inside the tile for the detection. The detection system is operating with a homodyne method, isolating only the frequency of operation and reducing or eliminating all the incoherent signals.