Optical Communication and Multi-Modal Energy Harvesting

Wireless sensor nodes have many compelling applications such as smart buildings, medical implants, and surveillance systems. However, existing devices are bulky, measuring >1cm, and they are hampered by short lifetimes and fail to realize the “smart dust” vision of [1]. Smart dust requires a mm-scale, wireless sensor node with perpetual energy harvesting. Recently two application-specific implantable microsystems [2][3] demonstrated the potential of a mm-scale system in medical applications. However, [3] is not programmable and [2] lacks a method for re-programming or re-synchronizing once encapsulated. Other practical issues remain unaddressed, such as a means to protect the battery during the time period between system assembly and deployment and the need for flexible design to enable use in multiple application domains. To this end, we propose a 1.0mm general-purpose heterogeneous sensor node platform with a stackable multi-layer structure that includes a new, ultra-low power IC (InterIntegrated Circuit) interface for inter-layer communication. The system has an ultra-low-power optical wakeup receiver and GOC (Global Optical Communication), which enables re-programming and synchronization. It also includes an ultra-low power PMU (Power Management Unit) with BOD (BrownOut Detector) to prevent processor malfunctions and battery damage. The BOD also controls a POR (Power-On Reset) module in other layers to enable a proper reset sequence. Image and temperature sensors are implemented, but the modularity of the system allows end-users to easily replace or add layers to incorporate specific circuits in appropriate technologies as needed.