We present the design, implementation, and evaluation of MiFly, a self-localization system for autonomous drones that works across indoor and outdoor environments, including low-visibility, dark, and GPS-denied settings. MiFly performs 6DoF self-localization by leveraging a single millimeter-wave (mmWave) anchor in its vicinity - even if that anchor is visually occluded. MiFly's core contribution is in its joint design of a mmWave anchor and localization algorithm. The low-power anchor features a novel dual-polarization dual-modulation architecture, which enables single-shot 3D localization. Mm Wave radars mounted on the drone perform 3D localization relative to the anchor and fuse this data with the drone's internal inertial measurement unit (IMU) to estimate its 6DoF trajectory. We implemented and evaluated MiFly on a DJI drone. We collected over 6,600 localization estimates across different trajectory patterns and demonstrate a median localization error of 7 cm and a 90thpercentile less than 15 cm, even in low-light conditions and when the anchor is fully occluded (visually) from the drone. Demo video: voutu.be/LfXfZ26tEok

The accurate localization and tracking of dynamic targets, such as equipment, people, vehicles, drones, robots, and the assets that they interact with in GPS-denied indoor environments is critical to enabling safe and efficient operations in the next generation of spatially-aware industrial facilities. This paper presents DragonFly, a 3D localization system of highly dynamic backscatter tags using a single MIMO mmWave radar. The system delivers the first demonstration of a mmWave backscatter system capable of exploiting the capabilities of MIMO radars for the 3D localization of mmID tags moving at high speeds and accelerations at long ranges by introducing a critical Doppler disambiguation algorithm and a fully-integrated cross-polarized dielectric-lens-based mmID tag consuming a mere 68 μW. DragonFly was extensively evaluated in static and dynamic configurations, including on a flying quadcopter, and benchmarked against multiple baselines, demonstrating its ability to track the positions of multiple tags with a median 3D accuracy of 12 cm at speeds and acceleration on the order of 10 m s–1 and 4 m s–2 and at ranges of up to 50 m.

Reliable 3D localization in dynamic and cluttered environments remains a significant challenge, particularly in indoor scenarios. DragonFly demonstrated the feasibility of accurate 3D localization using mmWave tags and a single commercial MIMO radar. However, in dynamic conditions, elevation estimates are often corrupted by outliers, especially during rapid accelerations(mostly due to vibrations) that exceed the system's maximum unambiguous radial acceleration threshold. To address this issue, we propose a novel correction framework that leverages a hypothesis testing procedure to detect and correct elevation outliers. The method tracks multiple candidate elevation trajectories over time, detects inconsistencies using a zig-zag pattern analysis, and resolves ambiguity through a likelihood ratio test based on elevation velocities modeled as a Gaussian distribution. Experiments conducted in highly cluttered environments with drones and mobile tags demonstrate that our method reliably aligns radar estimates with ground truth, successfully correcting 100% of outliers in the evaluated datasets.

Backscatter communication is an emerging paradigm for pervasive connectivity of low-power communication devices. Wirelessly powered backscattering wireless sensor networks (WSNs) become particularly important to meet the upcoming era of the Internet of Things (IoT), which requires the massive deployment of self-sustainable and maintenance-free low-cost sensing and communication devices. This article will introduce the state-of-the-art antenna design and radio frequency (RF) system integration for wirelessly powered backscatter communications, covering both the node and the base unit. We capture the latest development in ultralow-power RF front ends and coding schemes for$\mu \text{W}$-level backscatter modulators, as well as the latest progress in wireless power transfer (WPT) and energy harvesting (EH) techniques. Newly emerged rectenna system, waveform design, and channel optimization are reviewed in light of the opportunities for adaptively optimizing the WPT/EH efficiency for low-power signals with varying conditions. In addition, advanced device packaging and integration technologies in, e.g., additively manufactured RF components and modules for microwave and millimeter-wave ubiquitous sensing and backscattering energy-autonomous RF structures are reported. Inkjet printing for the sustainable and ultralow-cost fabrication of flexible RF devices and sensors will be reviewed to provide a prospective insight into the future packaging of backscatter communications from the chip-level design to complete system integration. Finally, this article will also address the challenges in fully wireless powered backscatter radio networks and discuss the future directions of backscatter communication in terms of “Green IoT” and “Low Carbon” smart home, smart city, smart skin, and machine-to-machine (M2M) applications.

Radio technologies are appealing for unobtrusive and remote monitoring of human activities. Radar-based human activity recognition proves to be a success, for example, Project Soli developed by Google. However, it is expensive to scale up for multiuser environments. In this article, we propose a solution—the HoloTag system—which circumvents the multichannel-radar scaling problem through the use of a quasivirtual ultralow-cost UHF RFID array over which a holographic projection of its environment is measured and used to both localize and monitor the health of several targets. The method is first described in detail, before the image reconstruction process, employing known beamforming algorithms—Delay & Sum, and Capon—is shown and its scaling properties simulated. Then, the idiosyncrasies of the implementation of HoloTag using low-cost off-the-shelf hardware are explained, before its ability to simultaneously measure the breathing rates and positions of multiple real and synthetic targets with accuracies of better than 0.8 bpm and 20 cm is demonstrated.

In this review, the particular importance and associated opportunities of additively manufactured radiofrequency (RF) components and modules for Internet of Things (IoT) and millimeter-wave ubiquitous sensing applications is thoroughly discussed. First, the current advances and capabilities of additive manufacturing (AM) tools are presented. Then, completely printed chipless radio-frequency identification (RFID) systems, and their current capabilities and limitations are reported. The focus is then shifted toward more complex backscattering energy autonomous RF structures. For each of the essential components of these structures, that encompass energy harvesting and storage, backscattering front ends, passive components, interconnects, packaging, shape-chaging (4-D printed) topologies and sensing elements, current trends are described and representative stateof- the-art examples reported. Finally, the results of this analysis are used to argue for the unique appeal of AM RF components and systems toward empowering a technological revolution of costefficient dense and ubiquitous IoT implementations.

Inkjet printing on flexible paper and additive manufacturing technologies (AMT) are introduced for the sustainable ultra-low-cost fabrication of flexible radio frequency (RF)/microwave electronics and sensors. This paper covers examples of state-of-the-art integrated wireless sensor modules on paper or flexible polymers and shows numerous inkjet-printed passives, sensors, origami, and microfluidics topologies. It also demonstrates additively manufactured antennas that could potentially set the foundation for the truly convergent wireless sensor ad-hoc networks of the future with enhanced cognitive intelligence and “zero-power” operability through ambient energy harvesting and wireless power transfer. The paper also discusses the major challenges for the realization of inkjet-printed/3-D printed high-complexity flexible modules as well as future directions in the area of environmentally-friendly “Green”) RF electronics and “Smart-House” conformal sensors.