The use of millimeter-wave (mmWave) bandwidth is one key enabler to achieve the high data rates in the fifth-generation (5G) cellular systems. However, mmWave signals suffer from significant path loss due to high directivity and sensitivity to blockages, limiting its adoption within small-scale deployments. To enhance the coverage of mmWave communication in 5G and beyond, it is promising to deploy a large number of reconfigurable intelligent surfaces (RISs) that passively reflect mmWave signals towards desired directions. With this motivation, in this work, we study the coverage of an RIS-assisted large-scale mmWave cellular network using stochastic geometry, and derive the peak reflection power expression of an RIS and the downlink signal-to-interference ratio (SIR) coverage expression in closed forms. These analytic results clarify the effectiveness of deploying RISs in the mmWave SIR coverage enhancement, while unveiling the major role of the density ratio between active base stations (BSs) and passive RISs. Furthermore, the results show that deploying passive reflectors are as effective as equipping BSs with more active antennas in the mmWave coverage enhancement. Simulation results confirm the tightness of the closed-form expressions, corroborating our major findings based on the derived expressions.

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RIS-Assisted Coverage Enhancement in Millimeter-Wave Cellular Networks

This review introduces several areas of importance in acoustic emission (AE) technology, starting from signal attenuation. Signal loss is a critical issue in any large-scale AE monitoring, but few systematic studies have appeared. Information on damping and attenuation has been gathered from metal, polymer, and composite fields to provide a useful method for AE monitoring. This is followed by discussion on source location, bridge monitoring, sensing and signal processing, and pressure vessels and tanks, then special applications are briefly covered. Here, useful information and valuable sources are identified with short comments indicating their significance. It is hoped that readers note developments in areas outside of their own specialty for possible cross-fertilization.

/pdf/review-on-structural-health-evaluation-with-acoustic-2yceo4jr7o.pdf

Review on Structural Health Evaluation with Acoustic Emission

A robust Bayesian methodology for damage localization in plate-like structures using ultrasonic guided-waves

In-flight and wireless damage detection in a UAV composite wing using fiber optic sensors and strain field pattern recognition

In this paper, ultrasonic attenuation of engineering materials is evaluated comprehensively, covering metals, ceramics, polymers, fiber-reinforced composites, wood, and rocks. After verifying two reliable experimental methods, 336 measurements are conducted and their results are tabulated. Attenuation behavior is determined over broadband spectra, extending up to 15 MHz in low attenuating materials. The attenuation spectra are characterized in combination with four power law terms, with many showing linear frequency dependence, with or without Rayleigh scattering. Dislocation damping effects are re-evaluated and a new mechanism is proposed to explain some of the linear frequency dependencies. Additionally, quadratic and cubic dependencies due to Datta–Kinra scattering and Biwa scattering, respectively, are used for some materials to construct model relations. From many test results, some previously hidden behaviors emerged upon data evaluation. Effects of cold working, tempering, and annealing are complex and sometimes contradictory. Comparison to available literature was attempted for some, but most often prior data were unavailable. This collection of new attenuation data will be of value in materials selection and in designing structural health monitoring and non-destructive inspection protocols.

A Comprehensive Report on Ultrasonic Attenuation of Engineering Materials, Including Metals, Ceramics, Polymers, Fiber-Reinforced Composites, Wood, and Rocks

The health monitoring of aerostructures assists performance enhancement of existing structures. Continuous monitoring and different techniques involved in the structural monitoring help to increase the efficiency of structures, postpone the failures, and provide the prototype for future aerospace structures with better durability. Structural performance of aerospace composites depends on strength, stiffness, yield capacity, bending capacity, resistance against corrosion, impact and lightning, and fatigue due to cyclic loading. In structural monitoring, the four different stages followed to monitor any damage in aerospace composite structure are operation evaluation, data accession, feature extraction, followed by statistical modeling. This chapter on structural health monitoring for aerostructures elaborates the methods to detect and prevent the failures in the structures, as observed through a series of literature available based on the type of damages and techniques to detect them like cracking, fiber pullout, delamination and shearography, eddy current method, transient thermographic method, etc, respectively. In this chapter structural health monitoring of composite aerostructures is reviewed in detail. Different techniques used to monitor the various failures occurring in the composite structures in aerospace industry are explained in detail. Structures made of composite material used in aerospace fail due to fiber-matrix damage. Hence, it is important to analyze such damage like fiber buckling, fiber splitting, fiber cracking, fiber fracture, and fiber bending, and cracks in the matrix etc. to prevent catastrophic results.

Structural health monitoring of aerospace composites

Experimental investigation on physical and mechanical properties of lime mortar: Effect of organic addition

The present study has been taken up to analyse the ancient plasters at Charminar, Hyderabad, India for the effective conservation of the historic monument. The plasters were characterized adopting physicochemical analysis as well as modern analytical techniques including XRD, TGA with DTA, SEM and Infra-Red methods (FT- IR). The binder is calcium rich lime with binder aggregate ratio of 1:2.75 to 1:3.43 by weight and mineralogical analysis reflect load bearing phases vaterite, calcite and aragonite with some amount of alumina silicates contributing to strength of the mortars. The results of FT-IR substantiated the outcome of organic test. TGA confirms the results of XRD and indicated the loss of weight around temperature of 750 °C showing decomposition of calcite and vaterite and release of CO2. SEM images validated the presence of calcite and vaterite. The organics present in the lime plasters in the form of carbohydrates and proteins has mitigated the degradation of materials that could be the main reason behind the sound survival of the Charminar over the ages. On fermentation, organics were converted into alcohols of short chain and stabilised the formation of meta stable vaterite rather than calcite. This keeps the mortars young and hence the durability of the structure.

Analysis of ancient lime plasters – Reason behind longevity of the Monument Charminar, India a study

The tradition of using lime as a binder has been in practice over the centuries and is cited in the architectural feats of all kinds of civilizations. Besides the basic ingredients of lime, sand an...

Effect of natural polymers from cissus glauca roxb on the mechanical and durability properties of hydraulic lime mortar

Influence of natural additives on mechanical and physical properties of hydraulic lime mortar has been investigated experimentally. Results revealed that organically modified lime mortar enhances the compressive strength significantly as it improved the bond between two consecutive lime particles in the matrix. Results also reflected that organically modified lime mortar with longer curing periods increased the compressive strength compared to reference mortar made of lime without organic addition. It is due to the presence of proteins and carbohydrates in the organic additives that influences the carbonation and hydraulic reaction in the lime matrix which helps to enhance the compressive strength of modified mortar. Addition of organic additives in lime mortar also reduces the porosity in the matrix and increases the hydrophobic nature and reduces water affinity of the hydraulic lime mortar.

S. Thirumalini

Papers

Structural health monitoring of aerospace composites

Experimental investigation on physical and mechanical properties of lime mortar: Effect of organic addition

Analysis of ancient lime plasters – Reason behind longevity of the Monument Charminar, India a study

Effect of natural polymers from cissus glauca roxb on the mechanical and durability properties of hydraulic lime mortar

Mechanical and physical properties of natural additive dispersed lime