3D-printed actuator-based beam-steering approach for improved physical layer security in visible light communication

Abstract

In this thesis, the design, manufacturing and implementation of a 3D-printed lens scanner-based beam-steering are presented for use in visible light communication (VLC) applications. The scanner, measuring 5 x 5 cm, is designed for low-cost 3D printing with fused deposition modeling using polylactic acid (PLA). The scanning is facilitated through electromagnetic actuation of the lens frame, carrying a conventional 25 mm lens in two nearly orthogonal directions. The serpentine spring that connects the lens frame to the external frame is tailored to offer similar spring constants in the directions of actuation, and minimal (< 1.5 mm) sag due to the mass of the lens. The manufactured actuator was integrated on a miniaturized VLC test-bed (70 cm x 40 cm x 40 cm). Using the test-bed, the applied voltage vs. beam displacement behavior of the actuator was characterized in the lateral plane, and beam-steering on a moving target was demonstrated with face-recognition feedback. The proposed scheme was targeted to offer an improved security measure in VLC through tracking the legitimate receiver (i.e. via face recognition) and using the feedback to steer the focused light onto the targeted device. The joint use of focusing and steering features allows for the legitimate receiver to roam within the room while enjoying the improved secrecy due to focused light. The secrecy capacity for the demonstrated approach was also calculated, which compares favorably to a number of jamming, spatial modulation and beam-forming counterparts. The presented actuator can be used with larger room dimensions, yet up-scaling to larger illumination units will require the use of a lens having a smaller focus to achieve a larger total steering angle. This thesis is composed of five different chapters. The concepts of visible light communication and light fidelity (Li-Fi) are introduced with a thorough literature review in the first chapter, while the techniques used in the thesis are also defined and presented. In the second chapter, the design of the actuator is described through definite computer-aided design (CAD) models and finite element analysis (FEA) simulations, while the experimental setup is also presented. Meanwhile, the demonstrations and the measurement results from the beam-steering operation of the actuator are presented in the third chapter. Then, the discussion section, based on the secrecy improvement through the use of the actuator and the up-scaling of the actuator to real-world dimensions, is presented in the fourth chapter. Finally, the fifth chapter presents the conclusions and further future work based on the actuator. Also, the details regarding the experiments conducted in Chapter 3, some of the designs of the actuator that were changed in order to obtain the final prototype and some discussion based on the mechanical stress on the actuator caused by the weight of the lens are presented in the Appendix section.