66 research outputs found
Extended geometry and gauged maximal supergravity
We consider generalized diffeomorphisms on an extended mega-space associated
to the U-duality group of gauged maximal supergravity in four dimensions, E_7.
Through the bein for the extended metric we derive dynamical (field-dependent)
fluxes taking values in the representations allowed by supersymmetry, and
obtain their quadratic constraints from gauge consistency conditions. A
covariant generalized Ricci tensor is introduced, defined in terms of a
connection for the generalized diffeomorphisms. We show that for any
torsionless and metric-compatible generalized connection, the Ricci scalar
reproduces the scalar potential of gauged maximal supergravity. We comment on
how these results extend to other groups and dimensions.Comment: 41 pages. v2,v3: minor changes and references adde
Energy-Sustainable IoT Connectivity: Vision, Technological Enablers, Challenges, and Future Directions
Technology solutions must effectively balance economic growth, social equity,
and environmental integrity to achieve a sustainable society. Notably, although
the Internet of Things (IoT) paradigm constitutes a key sustainability enabler,
critical issues such as the increasing maintenance operations, energy
consumption, and manufacturing/disposal of IoT devices have long-term negative
economic, societal, and environmental impacts and must be efficiently
addressed. This calls for self-sustainable IoT ecosystems requiring minimal
external resources and intervention, effectively utilizing renewable energy
sources, and recycling materials whenever possible, thus encompassing energy
sustainability. In this work, we focus on energy-sustainable IoT during the
operation phase, although our discussions sometimes extend to other
sustainability aspects and IoT lifecycle phases. Specifically, we provide a
fresh look at energy-sustainable IoT and identify energy provision, transfer,
and energy efficiency as the three main energy-related processes whose
harmonious coexistence pushes toward realizing self-sustainable IoT systems.
Their main related technologies, recent advances, challenges, and research
directions are also discussed. Moreover, we overview relevant performance
metrics to assess the energy-sustainability potential of a certain technique,
technology, device, or network and list some target values for the next
generation of wireless systems. Overall, this paper offers insights that are
valuable for advancing sustainability goals for present and future generations.Comment: 25 figures, 12 tables, submitted to IEEE Open Journal of the
Communications Societ
High-Power and Safe RF Wireless Charging: Cautious Deployment and Operation
The wired charging and the need for battery replacements are critical
barriers to unlimited, scalable, and sustainable mobile connectivity,
motivating the interest in radio frequency (RF) wireless power transfer (WPT)
technology. However, the inherently low end-to-end power transfer efficiency
(PTE) and health/safety-related apprehensions about the technology are critical
obstacles. Indeed, RF-WPT implementation and operation require efficient and
cautious strategies and protocols, especially when targeting high-power
charging, which constitutes the scope of this work. Herein, we overview the
main factors affecting the end-to-end PTE of RF-WPT systems and their
multiplicative effect and interdependencies. Moreover, we discuss key
electromagnetic field (EMF) exposure metrics, safety limits, and approaches for
efficient and EMF-aware deployment and operation. Quantitatively, we show that
near-field RF charging may significantly reduce EMF exposure, and thus must be
promoted. We also present our vision of a cyber-physical system for efficient
and safe wireless charging, specify key components and their interrelation, and
illustrate numerically the PTE attained by two modern low-power multi-antenna
architectures in a simple setup. Throughout the paper, we highlight the need
for high end-to-end PTE architectures and charging protocols transparently
complying with EMF exposure regulations and outline relevant challenges and
research directions. This work expands the vision and understanding of modern
RF-WPT technology and constitutes a step towards making the technology
attractive for worldwide commercial exploitation.Comment: 8 pages, 5 figures, 1 tabl
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