Ultra low-voltage low power backscatter communication and energy harvesting for long-range battery-free sensor tags

Abstract

To achieve economic viability across wide area deployments, many smart cities and agricultural sensing applications require wireless sensing and communication devices with long operating ranges of hundreds of meters to kilometers. Ideally, such sensors would be battery-free to enable unlimited lifetime. Prior work in RF-powered sensor networks has generally focused on achieving either long-range communication, or battery-free operation, but generally not both at the same time. The key system level challenges are the need for efficient RF power capture from incident RF signals, efficient RF power harvesting, and a low-power sensing and communication approach such as backscatter communication that enables data collection at the minimum possible power consumption. This thesis presents four systems that explore the key challenges in this space: (1) a 2.4 GHz RF energy harvesting system leveraging an ultra-low power timer to minimize the RF power required for acold-start; (2) an efficient reduced-size metal-mount sensor tag antenna; (3) a secure microcontroller-based sensor tag with a fiber-optic anti-tamper loop; and finally (4) a 5.8 GHz battery-free sensor tag that is operational at 1km range, having an RF power level of only -23 dBm (5μW) and a measured cold-start power-up voltage of only 15 mV. These systems each demonstrate innovative design elements that can be combined in different combinations to address challenging long-range,battery-free sensing and communication applications.