We present a simple freeform lens design method for an application to LED collimating illumination. The method is derived from a basic geometric-optics analysis and construction approach. By using this method, a highly collimating lens with LED chip size of 1.0 mm × 1.0 mm and optical simulation efficiency of 86.5% under a view angle of ± 5 deg is constructed. To verify the practical performance of the lens, a prototype of the collimator lens is also made, and an optical efficiency of 90.3% with a beam angle of 4.75 deg is measured.
Radio Frequency Identification (RFID) has recently played an important role in wireless sensing network. However, if multiple passive tags are simultaneously transmitted to the reader, the reader is unable to identify the tags. This will reduce the efficiency of a RFID system. To solve this problem, we propose a modified anti-collision algorithm based on ALOHA protocol to improve the performance in a RFID system. Simulation results show that the proposed algorithm is better than that of traditional method.
We propose a complementary optimization method to design a freeform lens for uniform illumination with extended LED sources. With this method, a primary freeform lens is first constructed based on a source-target energy mapping approach; then a complementary illuminance on the target plane is introduced to optimize the primary freeform lens so that it can produce uniform illumination with an extended COB LED. The computer simulation results show that the illuminance uniformity of the optimized lens can be improved nearby 30% as compared with that of the primary lens; meanwhile, the optical efficiency achieves above 94%.
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