Presented is a novel power management circuit for wireless sensor nodes that senses and processes a signal, and transmits an RF signal using scavenged energy without battery assistance. Experimental results show that with a single charging, it is possible for the sensor node to be activated by a wakeup pulse and deactivate itself after transmission of the RF signal to a receiver at a distance of 20 m every 5 min for 8 h without external power.Introduction: Advances in low-power electronic design and fabrication, along with the low duty cycle of wireless sensors, have reduced power requirements to the order of microwatts and promoted the possibility of microsensors and communication nodes that are powered by scavenged energy [1]. Since natural or artificial light and vibration is ubiquitous, solar cell and vibration-to-electricity converters seem to be the most appropriate power sources for the wireless ubiquitous sensor nodes [2][3][4]. To our knowledge, all currently reported wireless nodes powered by scavenged energy are activated when the storage capacitor charges to a certain pre-specified high energy level, and are deactivated when the stored energy has been depleted to a pre-specified low level [2,5,6]. However, owing to the existence of multiple sensor nodes and the energy being scavenged at random intervals in real-world applications, such random activation may cause signal collisions at the sink node. The deactivation process causes a much more serious problem, such that once the sensor node transmits the radio frequency (RF) signal, it cannot be activated again until the storage capacitor recharges. This means that, if the sensor node is powered by a solar cell, it does not operate at night. In this Letter we present a novel power management circuit that makes it possible to avoid data collision and to transmit multiple RF signals with a single charging, along with experimental results.
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