WEH: Energy Scavenging of Passive Tags with Unspecified Locations

In the full implementation of Internet of Things (IoT), we may have more than 30 sensors and ID tags in a common room, and more than 300 sensors/tags in a hospital room. In consideration of not only battery recharging but also recycling, the last layer of IoT needs to be passive to support this aggressive number scaling of pervasive tag deployment. This trend will be even more aggravated in the future Internet of Everything (IoET). Hence, energy scavenging of passive tags to support digital ID modulation and sensor readout is critical to realize the eventual IoT and IoET vision. Under the assumption of unspecified tag location within a zone of at least 5m, we will briefly discuss the advantages and limitations of the approaches by RF, thermoelectric, ultrasound/vibration, and solar cells. Following similar arguments, the operational range of modern RFID star network is often limited by the tag sensitivity, where the tag needs to harvest sufficient ambient energy to build the digital communication link. For the RF energy harvesting by charge pumping, we will then investigate the limitation set by the impinging energy and device nonlinearity which render the design tradeoffs between the energy efficiency and peak voltage. Last but not least, we will show how manufacturing variation of the diodes and passive devices can severely influence the harvesting performance and then present possible mitigation methods.