Energy Storage and Management System With Carbon Nanotube Supercapacitor and Multidirectional Power Delivery Capability for Autonomous Wireless Sensor Nodes

This paper presents an energy storage and management system to achieve long lifetime and miniaturization for autonomous wireless sensor nodes, which can be used in communication network for microgrids. The system employs supercapacitors to form a multienergy-source structure, and thus features multidirectional power delivery capability, which in turn allows the implementation of such state-of-the-art power management techniques as dynamic voltage scaling (DVS). A global energy management strategy is introduced to realize appropriate energy delivery, with the aid of a power management unit consisting of several proposed power converters that are capable of bidirectional operation. The bidirectional operation also dramatically increases the tracking speed during DVS with a charge-recycle technique. Fabrication of supercapacitor featuring compatibility with the CMOS process is also discussed, focusing on the preparation of free-standing single-walled carbon nanotube (CNT) films directly on a Si substrate, as electrodes for supercapacitor. A prototype of a dc-dc converter experimentally verifies the bidirectional operation and an improvement of over 30 times on tracking speed during DVS. Meanwhile, experiments on a CNT supercapacitor coin cell show high performances and excellent stability. The proposed designs provide the possibility of a fully on-chip energy system with the concept of heterogeneous integration.