Department of Applied Mechanics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

A two-dimensional numerical simulation of tandem wings flapping in inclined stroke plane kinematics is carried out. The distance between the two wings is varied to understand its effect on the vortex dynamics and dipole jet. Immersed boundary method is employed for the study. The change in instantaneous and average vertical force production of individual wings of the tandem wing configuration is compared to the single isolated wing. Further, various lift enhancement mechanism in the class of flows is understood. The alignment of dipole jet identified could be used in understanding the vertical force production of multiple flapping wings. © 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

World University root node

AIAA Scitech 2020 Forum

Numerical investigation of flapping wings in inclined stroke plane kinematics

In this, study, an attempt is made to differentiate muscle nonfatigue and fatigue condition using signal complexity metrics derived from phase space network features. A total of 55 healthy adult volunteers performed dynamic contraction of the biceps brachii muscle. The first and last curl are segmented and are considered as nonfatigue and fatigue condition respectively. A weighted phase space network is constructed and reduced to a binary network based on various radii. The mean and median degree centrality features are extracted from these networks and are used for classification. The results of the classification indicate that these features are capable of differentiating nonfatigue and fatigue condition with 91% accuracy. This method of analysis can be extended to applications such as diagnosis of neuromuscular disorder where fatigue is a symptom. © 2020 European Federation for Medical Informatics (EFMI) and IOS Press.

Studies in Health Technology and Informatics

Classification of biceps brachii muscle fatigue condition using phase space network features

In this paper, the development of a modified beamforming method, named as, Filtered Delay Weight Multiply and Sum (F-DwMAS) beamforming is reported. The developed F-DwMAS method was investigated on a minimum-redundancy synthetic aperture technique, called as 2 Receive Synthetic Aperture Focussing Technique (2R-SAFT), which uses one element in the transmit and two consecutive elements in the receive, for achieving high-quality imaging in low complex ultrasound systems. Notably, in F-DwMAS, an additional aperture window function is designed and incorporated to the recently introduced F-DMAS method. The different methods of F-DwMAS, F-DMAS and Delay and Sum (DAS) were compared in terms of Lateral Resolution (LR), Axial Resolution (AR), Contrast Ratio (CR) and contrast-to-noise ratio (CNR) in a simulation study. Results show that the proposed F-DwMAS resulted in improvements of LR by 22.86 % and 25.19 %, AR by 5.18 % and 11.06 % and CR by 152 % and 112.8 % compared to those obtained using F-DMAS and DAS, respectively. However, CNR of F-DwMAS was 12.3 % less compared to DAS, but 103.09 % more than F-DMAS. Hence, it can be concluded that the image quality improved by F-DwMAS compared to DAS and F-DMAS. © 2020 IEEE.

Proceedings - International Symposium on Biomedical Imaging

A Filtered Delay Weight Multiply and Sum (F-DwMAS) Beamforming for Ultrasound Imaging: Preliminary Results

The interfacial shear strength of polymer thin film coating on calcium–silicate–hydrate (C–S–H) or cement paste significantly depends on the time-point, from addition of water, when the polymer is coated. This is because the physico-chemical properties of C–S–H surface evolve over time as hydration progresses. The instant of coating thus determines the interfacial performance of a thin film coating in an organic-inorganic material system. In this work, we provide molecular insights into the interactions of poly(methyl methacrylate) (PMMA) functional groups with the pore solution calcium and bound substrate calcium present in hydrating C–S–H. The experimental observation reveals that PMMA thin film coated on second day of hydration exhibits larger interfacial shear strength than when coated on the 28th day. The possible reasons for this observations are: a) chemical crosslinking of two oxygen atoms from two different PMMA polymer chains by pore solution calcium ions and b) the physical interaction between double bond oxygen (O1) present in –COO functional group of PMMA with pore solution calcium. In this work, physical interaction between double bond oxygen (O1) present in –COO functional group of PMMA with pore solution calcium and substrate calcium in C–S–H is addressed.

Effect of pore solution calcium and substrate calcium on PMMA/cement paste interface during early stages of hydration

Compressed Sensing (CS) has been applied by a few researchers to improve the frame rate of synthetic aperture (SA) ultrasound imaging. However, there appear to be no reports on reducing the number of receive elements by exploiting CS approach. In our previous work, we have proposed a strategic undersampling scheme based on Gaussian distribution for focused ultrasound imaging. In this work, we propose and evaluate three sampling schemes for SA to acquire RF data from a reduced number of receive elements. The effect of sampling schemes on CS recovery was studied using simulation and experimental data. In spite of using only 50% of the receive elements, it was found that the ultrasound images using the Gaussian sampling scheme had comparable resolution and contrast with respect to the reference image obtained using all the receive elements. Thus, the findings suggest a possibility to reduce the receive channel count of SA ultrasound system without practically sacrificing the image quality. © 2020 IEEE.

Department of Mechanical Engineering

Compressed Sensing for Data Reduction in Synthetic Aperture Ultrasound Imaging: A Feasibility Study

It is known that the elasticity of liver reduces progressively in the case of diffuse liver disease. Currently, the diagnosis of diffuse liver disease requires a biopsy, which is an invasive procedure. In this paper, we evaluate and report a noninvasive method that can be used to quantify liver stiffness using quasi-static ultrasound elastography approach. Quasi-static elastography is popular in clinical applications where the qualitative assessment of relative tissue stiffness is enough, whereas its potential is relatively underutilized in liver imaging due to lack of local stiffness contrast in the case of diffuse liver disease. Recently, we demonstrated an approach of using a calibrated reference layer to produce quantitative modulus elastograms of the target tissue in simulations and phantom experiments. In a separate work, we reported the development of a compact handheld device to reduce inter- and intraoperator variability in freehand elastography. In this work, we have integrated the reference layer with a handheld controlled compression device and evaluate it for quantitative liver stiffness imaging application. The performance of this technique was assessed on ex vivo goat liver samples. The Young’s modulus values obtained from indentation measurements of liver samples acted as the ground truth for comparison. The results from this work demonstrate that by combining the handheld device along with reference layer, the estimated Young’s modulus value approaches the ground truth with less error compared with that obtained using freehand compression (8% vs. 15%). The results suggest that the intra- and interoperator reproducibility of the liver elasticity also improved when using the handheld device. Elastography with a handheld compression device and reference layer is a reliable and simple technique to provide a quantitative measure of elasticity. © The Author(s) 2020.

Department Of Biotechnology

Fulltext

Ultrasonic Imaging

Toward Quantitative and Operator-independent Quasi-static Ultrasound Elastography: An Ex Vivo Feasibility Study

A dielectric-barrier discharge (DBD) in an argon–water mixture is applied to plasma pretreatment (PP) of amorphous silica for subsequent vapor-phase silanization (VS) in the same reactor. Comparison of amino-silanization of silica fiber-optic biosensor probes using a PP/VS sequence with strategies involving wet-chemical pretreatment or silanization shows a considerable improvement in reproducibility by the completely dry process. Practical applicability is demonstrated by an immunoassay with human immunoglobulin G as analyte. Thanks to the advantages of shorter processing time, avoidance of washing steps, and improved reproducibility, PP/VS is highly promising for industrial use.

Argon–water DBD pretreatment and vapor‐phase silanization of silica: Comparison with wet‐chemical processes

Geometrically modified fiber optic sensors (FOS), particularly U-bent FOS, have gained significant attention due to their remarkably high refractive index (RI) and evanescent wave absorbance (EWA) sensitivity, as well as their ergonomic design and ease in handling. In this article, we present a theoretical model for the U-bent FOS probes to predict the sensor behavior by numerically simulating the light propagation in an equivalent 2D semi-circular ring using ray tracing approach. In addition to the effects due to the modification of geometry, this article presents a thorough investigation of the influence of the bend-induced material deformation on the nature of light propagation and refractive losses. We introduce 'bend ratio' (ratio of bend radius to fiber core radius) to explain the influence of geometry modification and the bend-induced inhomogeneity in RI (BIRI) of the fiber core on RI sensitivity. The bend ratio of bent plastic optical fiber sensors falls under one of the four bending regimes, namely, gentle, geometric, saturation, and plastic, for which the bend ratios are less than ∼35, ∼25, 17, and 7, respectively. The results also show that for bend ratios less than 7, BIRI inhomogeneity is responsible for the high RI sensitivity observed with U-bent probes as opposed to the simple geometric modification. This article also indicates the existence of an optimum bend ratio (for a given value of RI of the surrounding medium) where RI sensitivity is maximum. These findings were validated with previously reported experimental results. © 2020 IEEE.

Journal of Lightwave Technology

Investigating the Refractive Index Sensitivity of U-Bent Fiber Optic Sensors Using Ray Optics

Cluster-assembled solids (CASs) formed by the self-assembly of monodispersed atomically precise monolayer-protected noble metal clusters are attractive due to their collective properties. The physical stability and mechanical response of these materials remain largely unexplored. We have investigated the mechanical response of single crystals of atomically precise dithiol-protected Ag29 polymorphs, monothiol-protected Ag46, and a cocrystal of the latter with Ag40 (formulas of the clusters have been simplified merely with the number of metal atoms). The Ag29 polymorphs crystallize in cubic and trigonal lattices (Ag29 C and Ag29 T, respectively), and Ag46 and its cocrystal with Ag40 crystallize in trigonal and monoclinic lattices (Ag46 T and Ag40/46 M, respectively). The time and loading-rate-dependent mechanical properties of the CASs are elucidated by measuring nanoindentation creep and stress relaxation. The obtained Young's modulus (Er) values of the CASs were similar to those of zeolitic imidazolate frameworks (ZIFs) and show the trend Ag29 T &gt; Ag29 C &gt; Ag40/46 M &gt; Ag46 T. We have also studied the viscoelastic properties of all of the four CASs and found that the value of tan damping factor of monothiol-protected Ag46 T was higher than that of other CASs. The unusual mechanical response of CASs was attributed to the supramolecular interactions at the surface of nanoclusters. This observation implies that the stiffness and damping characteristics of the materials can be modulated by ligand and surface engineering. These studies suggest the possibility of distinguishing between the crystal structures using mechanical properties. This work provides an understanding that is critical for designing nanocluster devices capable of withstanding mechanical deformations. Copyright © 2020 American Chemical Society.

Department of Electrical Engineering

Department Of Chemistry

Chemistry of Materials

Manifestation of Structural Differences of Atomically Precise Cluster-Assembled Solids in Their Mechanical Properties

In conventional focused beamforming (CFB), there is a known tradeoff between the active aperture size of the ultrasound transducer array and the resulting image quality. Increasing the size of the active aperture leads to an increase in the image quality of the ultrasound system at the expense of increased system cost. An alternate approach is to get rid of the requirement of having consecutive active receive elements and instead place them in a random order in a larger aperture. This, in turn, creates an undersampled situation where there are only M active elements placed in a larger aperture, which can accommodate N consecutive receive elements (with M < N). It is possible to formulate and solve the above-mentioned undersampling situation using a compressed sensing (CS) approach. In our previous work, we had proposed Gaussian undersampling strategy for reducing the number of active receive elements. In this work, we introduce a novel framework, namely Gaussian undersampling-based CS framework (GAUCS) with wave atoms as a sparsifying basis for CFB imaging method. The performance of the proposed method is validated using simulation and in vitro phantom data. Without an increase in the active elements, it is found that the proposed GAUCS framework improved the lateral resolution (LR) and image contrast by 27% and 1.5 times, respectively, while using 16 active elements and by 39% and 1.1 times, respectively, while using 32 active elements. Thus, the GAUCS framework can play a significant role in improving the performance, especially, of affordable point-of-care ultrasound systems. © 1986-2012 IEEE.