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Reconfigurable Intelligent Surfaces: Simplified-Architecture Transmitters—From Theory to Implementations
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| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 110 (No. 9) |
| Halaman | : | 1266-1289 |
| Abstrak | : | Reconfigurable intelligent surfaces (RISs) offer an entirely new route to alter the propagation properties of electromagnetic waves and thus control their reflection, refraction, and scattering features in arbitrary manners. Such physical attributes are perceived to bring about fundamental influence on the modern wireless communication system due to the possibilities to establish artificial and controllable propagation environments for radio signals, which no longer rely on the complex encoding, decoding, and other signal processing techniques. Recent studies reveal that the wave manipulation is not the only skill of the RISs. With the rapid developments of space–time digital metasurface and information metasurface, there has been increasing attention focused on the information manipulation via these artificial surfaces. In this article, we provide an overview of the theoretical models of the space–time digital metasurface and information metasurface, the mechanisms of wavefront shaping, and the signal modulations in space and time domains during the wave–matter interactions. We will also address some practical issues during implementations of the reconfigurable intelligent metasurfaces and the associated hardware architectures at microwave frequencies to realize simplified radio frequency transmitters. Several modulation schemes and the corresponding demonstration systems are introduced to illustrate the powerful abilities of the reconfigurable intelligent metasurfaces. Potential research directions of this technique are briefly discussed for their potential applications in future wireless networks. |
MIMO Evolution Beyond 5G Through Reconfigurable Intelligent Surfaces and Fluid Antenna Systems
| Pengarang | : | Arman Shojaeifard |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 110 (No. 9) |
| Halaman | : | 1244-1265 |
| Abstrak | : | With massive deployment, multiple-input–multiple-output (MIMO) systems continue to take mobile communications to new heights, but the ever-increasing demands mean that there is a need to look beyond MIMO and pursue the next disruptive wireless technologies. Reconfigurable intelligent surface (RIS) is widely considered a key candidate technology block to provide the next generational leap. The first part of this article provides an updated overview of the conventional reflection-based RIS technology, which complements the existing literature to include active and semiactive RIS, and the synergies with cell-free massive MIMO (CF mMIMO). Then, we widen the scope to discuss the surface-wave-assisted RIS that represents a different design dimension in utilizing metasurface technologies. This goes beyond being a passive reflector and can use the surface as an intelligent propagation medium for superb radio propagation efficiency. The third part of this article turns the attention to the fluid antenna, a novel antenna technology that enables a diverse form of reconfigurability that can combine with RIS for ultrahigh capacity, power efficiency, and scalability. This article concludes with a discussion of the potential synergies that can be exploited between MIMO, RIS, and fluid antennas. |
When Negative Is Not “Less than Zero”: Electric Charge as a Signed Quantity
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 59 (No. 4) |
| Halaman | : | 253-256 |
| Abstrak | : | Electromagnetism (E&M) is often challenging for students enrolled in introductory college-level physics courses. Compared to mechanics, the mathematics of E&M is more sophisticated and the representations are more abstract. Furthermore, students may lack productive intuitions they had with force and motion. In this article, we explore the mathematization of electric charge. Specifically, we explore how difficulties with positive and negative signs can arise for learners who approach integers primarily as positions on a number line. We discuss the nuances of electric charge as a physical quantity and situate it in a body of work by mathematics and physics education researchers to characterize the uses and meanings of signs. We then describe preliminary research that illustrates the effect of wording differences on student reasoning about electric charge as a signed quantity. Finally, we discuss implications for instruction. |
Theory, Analysis, and Design of Metasurfaces for Smart Radio Environments
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 110 (No. 9) |
| Halaman | : | 1227-1243 |
| Abstrak | : | The term “metasurface” (MTS) denotes an artificial surface constituted by a distribution of electrically small elements that collectively exhibit equivalent homogeneous boundary conditions (BCs) to an interacting electromagnetic field. MTSs are becoming increasingly popular due to the technological simplification that they offer with respect to volumetric metamaterials. In this article, we review the basic theory behind microwave MTSs seen as reconfigurable intelligent surfaces (RISs), oriented to the future visionary challenge of a smart radio environment. To this end, two different typologies of MTS are reviewed: surface-wave-based MTSs and nonspecular reflective MTSs. Both types can be effectively characterized using simplified problems that locally match the homogenized, modulated BCs. A different use of these problems allows for an accurate design of radiated and scattered fields. An accurate ray representation is also suggested, which allows for an effective description of the scattered field also in the Fresnel region and for the insertion of the MTS description in ray-tracing tools for network planning. Several examples of practical implementation are shown, and the challenges in applying electronic reconfigurability are discussed. |
A Rotational Dynamics Laboratory Upgrade
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 59 (No. 4) |
| Halaman | : | 250-252 |
| Abstrak | : | In our first-semester introductory physics laboratory, we have an exercise on rotational dynamics. We have recently upgraded the equipment that we use in that exercise without changing the actual exercise. The new equipment has performed well so far, and we wanted to share what we did with others who may be looking for a relatively inexpensive way to outfit a laboratory on rotational dynamics. We will describe the physics of the exercise and what we ask our students to do. We will describe the components we purchased, what they cost, and how we assembled the apparatus. Finally, we will present some results from the exercise using the apparatus we built. |
Wavefront Shaping for Wireless Communications in Complex Media: From Time Reversal to Reconfigurable Intelligent Surfaces
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 110 (No. 9) |
| Halaman | : | 1210-1226 |
| Abstrak | : | Reconfigurable intelligent surfaces (RISs) are gaining huge momentum in the field of wireless communications due to the paradigm shift that they bring. Indeed, they allow making any environment electromagnetically smart and dynamically reconfigurable for more efficient and greener wireless communications. As physicists, we proposed to use electronically tunable metasurfaces to shape the electromagnetic waves carrying our wireless communications in reflection almost ten years ago, inspired by some works that we and colleagues did in the field of wave control in complex media. In this article, we review the seminal works that led us to propose this concept, starting from the original one that is time reversal. Then, we propose a physicist’s point of view of RISs using a comparison with phase conjugation. Finally, we highlight what we think are their limitations, relying on both our knowledge of wave control and our study of them over a decade. |
A Race Between Rolling and Sliding Up and Down an Incline
| Pengarang | : | Carl E. Mungan |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 59 (No. 4) |
| Halaman | : | 247-249 |
| Abstrak | : | Races between moving objects are an engaging way to teach dynamics to introductory physics students. One standard example consists in racing hollow and solid cylinders as they roll down an inclined plane. Another striking demonstration is a race between two marbles on side-by-side tracks that start and end together, but with one track taking a straight path and with the other following a cycloidal shape. In the present article, two objects (having the same mass and shape) are launched from the same starting height with the same speed up an inclined plane. One of the objects is subject to kinetic friction. The other object is not because it rolls without slipping on wheels along the incline with negligible rolling friction. Each object travels upward, slows down, and then turns around and retraces its path to its starting point. If the two objects are launched simultaneously, which one makes it back first? |
Communication Models for Reconfigurable Intelligent Surfaces: From Surface Electromagnetics to Wireless Networks Optimization
| Pengarang | : | Marco Di Renzo |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 110 (No. 9) |
| Halaman | : | 1164-1209 |
| Abstrak | : | A reconfigurable intelligent surface (RIS) is a planar structure that is engineered to dynamically control the electromagnetic waves. In wireless communications, RISs have recently emerged as a promising technology for realizing programmable and reconfigurable wireless propagation environments through nearly passive signal transformations. With the aid of RISs, a wireless environment becomes part of the network design parameters that are subject to optimization. In this tutorial article, we focus our attention on communication models for RISs. First, we review the communication models that are most often employed in wireless communications and networks for analyzing and optimizing RISs and elaborate on their advantages and limitations. Then, we concentrate on models for RISs that are based on inhomogeneous sheets of surface impedance and offer a step-by-step tutorial on formulating electromagnetically consistent analytical models for optimizing the surface impedance. The differences between local and global designs are discussed and analytically formulated in terms of surface power efficiency and reradiated power flux through the Poynting vector. Finally, with the aid of numerical results, we discuss how approximate global designs can be realized by using locally passive RISs with zero electrical resistance (i.e., inhomogeneous reactance boundaries with no local power amplification) even for large angles of reflection and at high power efficiency. |
Rotation of Spherical Magnet Falling Through a Slit Copper Pipe
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 59 (No. 4) |
| Halaman | : | 243-246 |
| Abstrak | : | The stately fall of magnets through conducting pipes is a favorite classroom and laboratory activity used in teaching electromagnetic induction, Lenz’s law, eddy currents, electromagnetic braking, and even Newton’s third law. |
Survey on Fully Homomorphic Encryption, Theory, and Applications
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 110 (No. 10) |
| Halaman | : | 1572-1609 |
| Abstrak | : | Data privacy concerns are increasing significantly in the context of the Internet of Things, cloud services, edge computing, artificial intelligence applications, and other applications enabled by next-generation networks. Homomorphic encryption addresses privacy challenges by enabling multiple operations to be performed on encrypted messages without decryption. This article comprehensively addresses homomorphic encryption from both theoretical and practical perspectives. This article delves into the mathematical foundations required to understand fully homomorphic encryption ( FHE ). It consequently covers design fundamentals and security properties of FHE and describes the main FHE schemes based on various mathematical problems. On a more practical level, this article presents a view on privacy-preserving machine learning using homomorphic encryption and then surveys FHE at length from an engineering angle, covering the potential application of FHE in fog computing and cloud computing services. It also provides a comprehensive analysis of existing state-of-the-art FHE libraries and tools, implemented in software and hardware, and the performance thereof |