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CENTER FOR NON DESTRUCTIVE EVALUATION

RESEARCH THEMES

Ubiquitous Sensing

Redefining Material State Awareness

The current state of the art in fiber optic sensing relies on Fiber Bragg Grating and similar discrete sensing elements. While effective for localized measurements, they face scalability challenges in large-area monitoring due to increased complexity and cost. Continuous sensing provides a more efficient alternative, enabling measurements along the entire sensing medium. Existing distributed techniques, such as Rayleigh scattering, offer wide coverage but are limited in spatial resolution. Piezoresistive nanocomposites, such as GNP-doped PMMA, present a complementary approach by enabling conformal, surface-level sensing. SEM analysis reveals flake-like GNPs (~20–50 µm) forming partially interconnected conductive networks within the matrix. These networks are sensitive to mechanical deformation, where changes in inter-particle spacing lead to measurable variations in electrical resistance, enabling effective monitoring of damage evolution. Recent advances in fiber optic sensing and ultrasonic waveguide technologies at the Centre for Non-Destructive Evaluation (CNDE) further address these limitations by improving both resolution and operational range. Developments such as high-resolution distributed acoustic sensing (DAS) and waveguide-based ultrasonic measurements at temperatures up to 1400 °C significantly expand sensing capabilities. Together, these approaches point toward next-generation sensing paradigms that combine large-area coverage, high resolution, and enhanced environmental robustness, transforming materials and structures into truly ubiquitous sensing systems.

Structured Materials for Imaging

Metamaterials-based Ultrasonic/Acoustic imaging & sensors

• The CNDE group has been a leader in the field of employing meta-crystals and meta-materials for realizing extraordinary properties in imaging, vibration damping and mode filtering. This sub-theme will take a leap forward from these efforts, to achieve next generation sensing and device capabilities. In keeping with the goals of NDE 5.0, this sub-theme will explore technologies that can be integrated and embedded into structural members, such that self-sensing and self-warning capabilities can be in-built into them. Topological devices such as material-contrast and step-change lenses will be explored for integration into structural and machine elements, such that using passive excitation consisting of random external vibrations, local defect generation events can be flagged for immediate attention soon after a threshold indication. This process requires studying mechanical filtering mechanisms such that coherent information can be extracted from such random excitations. Once extracted, the signals will trigger an alarm through excitation of electromagnetic indicators for remote logging. The other broad topic that will be studied under this sub-theme, is that of metamaterial-based material sensors for online materials characterization. For example, integration of metamaterial layers into the walls of sensitive locations such as fuel or water tanks will be explored such that the level of toxic/ unwanted contaminants can be self-monitored, triggering an alarm beyond a threshold. Another example is the incorporation of metamaterial ridges into piping, wiring and cabling to achieve self-sensing and self-warning using passive random excitation, while embedded bandgap layers for blocking vibration and seismic disturbances is the other topic to be studied. These topics also contribute to the overall NDE 5.0 theme of ‘ubiquitous and distributed sensing and mitigation’

Meta-materials-based Electro-Magnetic (EM) imaging & sensors

• Conventional microwave and EM NDE employ waveguide-b dielectric and non-metallic composites. Information obtained using microwave sensors are used for determining material properties such as permittivity and permeability, material density, glass transition temperature, level, humidity for real time non-contact process monitoring. Other applications of microwave in the field of NDE are detection of voids, delamination, dislocations and layer thickness measurements in layered dielectric media and non-metallic heterogeneous composites. The major bottle neck in microwave NDE are the large dimensions and spatial resolution. This can be addressed using EM metamaterial surfaces which can enhance the coupled EM field strength between a sensor and the material under test (MUT). In this proposal, we will explore and develop novel engineered EM metamaterials to enhance the efficiency of the sensors and improve spatial resolution of microwave imaging.

Edge Intelligence & Soft-Sensing

AI enabled super-fast computations

• Currently, numerical computational methods such as Finite Element, Finite Difference, Finite Volume, Boundary Element, etc. are extensively used for calculations. However, the speed of computation and the resource requirements will necessitate the off-line mode of computation. In this proposed work, a disruptive approach to exploring the translation of these numerical calculations to the edge computing platforms such as GPUs and TPUs will be demonstrated for very sophisticated calculations. This is a relatively new paradigm with very limited literature available. The CNDE group has been developing this approach over the past 2 years and have achieved more than 7 orders of magnitude reduction in computational time and with very small computational resources for classic problems in stress, thermal, and flow analysis. In this work, the numerical models are used to train a sophisticated AI engine using a range of computational models. The trained AI engine is expected to then provide, near instant, calculations in edge computing platforms. Up until now, about 1000% extrapolation has been demonstrated on 2D and 3D Problem sets. Using this approach, edge problem solving will be explored to enhance the last mile intelligence at the sensor end and provide real-time problem solving capability to the sensors. This, to the best of our knowledge, has never been attempted.

Physics and Data based Soft Sensing Algorithms and Devices

• The technology of soft-sensing using physically based numerical models will be explored in order to enhance the fidelity of the sensor data. Currently, the spatial density of the data points often defines the fidelity of the information. However, using physical based models, it is expected that the special information can be enhanced with limited special density of measurements. It is also expected that this will also be useful to extrapolate the information to locations where measurements cannot be made due to the hostile environment or limitations in access. Again, very limited literature is currently available in this domain.

Pervasive Inspection

Wide Multi-spectral Imaging (Ultrasound, THz, IR, X-ray)

• Generating the image of an object in 2D and 3D using acoustic/elastic/electromagnetic waves has emerged as an invaluable aid for non-destructive evaluation of the object. Highly resolved images result only when spatial and temporal information are rich on multiple scales. Spectral and spatial resolution in imaging are constrained by bandwidth and field of view on the one hand, and illumination and collection efficiencies on the other. At every wavelength employed, sub-wavelength features are desirable but difficult to obtain through conventional imaging modalities. Obtaining well-resolved images is currently not feasible in all the spectral domains and time-consuming wherever it has been recently demonstrated. The plan at CNDE would be to develop generic computational imaging tools in conjunction with metamaterial components and machine learning algorithms to address the challenges.

Quantum Phononics

• The concept of imaging at depths with high resolution has been of much interest to scientists for decades. However even today, most technique available for very high resolution imaging are restricted to ultrathin materials or surfaces. Moreover typically being based on electromagnetic waves, such methods also often carry the risk of ionizing radiation when the depth of penetration has to be increased. The Phonon spectrum offers rich opportunities for imaging and communications at depths, but suffers from the challenge of poor resolution and noise. Although the use of metamaterials in recent years has allowed breaking down resolution limits (with CNDE itself contributing the best reported values in the ultrasonic domain at 1/72 of the operating wavelength), ultimately the only way to reach subnanometer resolutions is to reach the supra-hypersonic frequency range. However at these frequencies, we are hobbled by shot noise in the source, besides material noise inside the medium being interrogated. Here is where quantum technologies offer enormous promise, where single or ‘antibunched’ Phonon excitations are expected to overcome the shot-noise, while entanglement offers the tantalizing prospect of noise-cancelled imaging. Quantum Phononics may finally enable us to image at subnanometer resolutions at micrometer depths. On the other hand, with their natural ability to harness waste heat and vibration, Quantum Phononic networks could be elegantly integrated into existing structures and devices. With Phononic Quantum computing and logic devices, pervasive integration of ultrahigh precision sensing is a tantalizing possibility. The investigations will involve the development of sources for single and entangled phonons, as well as phononic logic and computing devices.

Remote Large Area Inspection

Intelligent Infrastructure (civil and industrial)

• CNDE is a world leader in developing health monitoring solutions for both civil and industrial structures. This sub-theme will massively build upon CNDE efforts in embedded waveguided approaches for achieving intelligent and self-sensing building materials. Sleeved rebar structures already used extensively in concrete structures will be the primary vehicle of these studies. By introducing de-sleeved regions at periodic target locations, and making using of the rebars as acoustic waveguides, this project will study the possibility of online monitoring of the health of concrete and composites. In applications ranging from bridge piles, building pillars, composite pipes and aircraft wing assemblies, this sub-theme will study the introduction of such ‘de-sleeve sensors’ for periodic internal imaging of the structures. The investigations will involve the embedment and study of single, periodically and randomly multiple sleeve-de-sleeve waveguides into structural members.

Nano-structured coatings

•The use of nano-structured multi-layered coating is proposed here using CNT and Graphene hybrid nano-structures with magnetic and conducting nano-particle decorations. The different layers of the coatings will be used to provide directional property measurements such as strain. The CNDE at IITM has previously reported on the development of these hybrid structures using CNTs that connect Graphene sheets to provide un-precedented strain measurement gage factors exceeding 115. This work was the first ever report that exceeded a gage factor of 100. The CNDE group has now been exploring this high strain measurements into wearables including gloves, fabric, etc. In this proposal, it is envisaged to extend this work in the area of development of sensor coatings that will provide a complete stress state on the surface using directional strain sensing using the decorated nano-structured materials to be developed.

CENTER FOR

NON-DESTRUCTIVE EVALUATION

Email: cnde@smail.iitm.ac.in

Phone: 044 2257 5688

Room 312, Machine Design Section,

Indian Institute of Technology Madras

Chennai 600036 India

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