Recent advances in micro-electromechanical systems (MEMSs) technology have enabled the design of low-power lowcost smart sensors equipped with multiple onboard functions such as sensing, computing, and communications. Such intelligent devices networked through wireless links have been referred to as wireless sensor networks and recognized as one of the most important technologies for the 21st century. Wireless sensor networks hold the promise to revolutionize the sensing technology for a broad spectrum of applications, including infrastructure monitoring and surveillance, disaster management, monitoring the health status of humans, plants, animals, and industrial machines, and so forth.