Hybrid Supplies for Wireless Micro-Systems

Ultra-compact micro-electronic devices like wireless micro-sensors provide sensing and monitoring functions to a wide variety of applications in medicine, industry, and the military. Because of their diminutive micro-scale dimensions, these micro-systems are unobtrusive and can be deployed in numerous quantities as a network gathering information from typically inaccessible environments, such as inside the human body [1]-[2]. The problem is the inaccessibility and ubiquity of the constituent nodes render the upkeep of the on-board energy supply impractical, forcing the device to sustain itself from whatever energy it was able to store initially. This is a significant challenge because typical micro-scale energy sources do not feature the necessary energy densities to fully supply practical systems capable of sensing, storing, computing, and transmitting data for extended lifetimes [3]. As a result, micro-scale devices suffer from short operational lives, as determined by the amount of energy initially stored in their small volumes [1], [4]. An effective strategy for prolonging life is to decrease the average power consumed in the system by duty-cycling and offsetting power-intensive tasks. For instance, sensing and wireless communication functions need not engage continuously or simultaneously. Performing these functions periodically or asynchronously (on demand) and allowing the system to idle often, as shown in Figure 1, reduce average power (PAverage) and therefore drain the energy