UC San Diego

The wireless sensor market has undergone explosive growth worldwide increasing to 18.78 billion USD in 2023 from 15.57 billion in 2022 to an expected rise to 105.18 billion in 2032. The excitement driving this market growth stems from the Internet of Things (IoT) revolution which has promised low-cost, compact, and “invisible” sensors which can integrate seamlessly into already existing systems. These IoT devices would bring enhanced industrial automation, improved wireless communications, environmental monitoring, and smart home capabilities to name a few. The IoT revolution, however, has fallen short in its promises due to the dependence on under-performing hardware designs which either require batteries, exhibit low data rates, or operate at significantly smaller ranges than their non IoT counterparts. To mitigate some of these issues, low power IoT (\ie coin-cell operated) or battery-free (\ie power harvesters) solutions have been proposed. These devices may provide improved sensing and communication ranges and data-rates however, they still lack scalability, cost, or seamless integration to many everyday systems. Technological saturation due to the increased number of IoT sensors and devices can hinder already existing systems and drive up the costs of everyday items. To mitigate the issue, fully-passive, battery-free solutions have been investigated to improve the range, data rate and cost of many common IoT applications.

This dissertation delineates several contributions to the existing body of knowledge in communication and sensing using completely passive devices. First, it describes a mmWave automotive radar smart-surface which can be decoded as drivers pass by. The system utilizes a novel data-encoding mechanism which leverages the spatial distribution of van-atta arrays to encode On-Off-Keying data bits. Secondly, this dissertation introduces a unique UHF wireless keypad interface which uses resonant RF stubs to encode deterministic buttons. This approach allows for easy-to-use deterministic button presses which can withstand severe multi-path and blockages. Previous systems used complicated swiping gestures which are difficult to memorize and are heavily impacted by environmental factors. Lastly, the dissertation presents new uses to reflect-arrays and meta-surfaces for enhancing non-line-of-sight communication and sensing and between multiple mediums.