2003-2006

(NTU Research Scholarship & Grant)

Below, you'll find our Projects organized by year. For questions on any specific Project or publication, feel free to contact me, and I will respond as soon as possible.

During My PhD

2003-04

Impedance-Based Concrete Monitoring: My First PhD Project

Ah, 2003. The year I first stepped into the lab, a fresh-faced PhD student with a mixture of nerves and unbridled excitement. My initial mission: to delve into the world of concrete health monitoring using something called PZT sensors and the electromechanical (EM) impedance technique. Little did I know, this foundational foray, culminating in a paper published in 2010, would become a dramatic lesson in the complexities of real-world engineering.

The Vision: A "Very Easy Method"

The core idea was elegantly simple, at least on paper. We aimed to embed tiny piezoelectric transducers (PZT) directly into concrete. These smart sensors would then emit EM admittance signatures when an electric field was applied. Any shift in these signatures over time would, in theory, reveal disturbances or damage within the concrete. The allure was clear: embedded sensors offered durability and protection from external elements—no more worrying about surface wear or vandalism.

The Reality: Concrete Challenges

But "simple" quickly gave way to "complex." Embedding PZT sensors in concrete proved to be a far cry from surface bonding. We grappled with critical questions: How do we ensure a robust bond between the PZT and the host concrete? How would the delicate sensors withstand the immense curing pressures and temperatures of fresh concrete? The challenge intensified when we considered that PZT sensors, while effective for metals, were known to be less so for non-metals like concrete. This was where the drama began to unfold.

The Breakthrough: Double Protection

This wasn't just about a scientific problem; it was about the resilience of a young researcher facing their first major hurdle. We needed an innovative solution, something to bridge the gap between the PZT's sensitivity and concrete's demanding environment. And then it hit us: a double protection wrap method.

We envisioned a dual-layer shield. The first layer would be a steel wire mesh, acting as a crucial bonding connector between the PZT and the surrounding concrete. This metal-to-metal connection was key. The second layer was a meticulous application of cement paste, creating a seamless bond between the wire mesh and the concrete host. It was an ingenious blend of metal and non-metal, a symphony of materials designed to give our embedded PZT the best possible chance.

The Verdict: Lab Validation and Statistical Triumph

With our double-protected PZT sensors, we embarked on the painstaking process of implementing and testing them on various lab-sized concrete cubes. Each signature recorded, each deviation observed, brought us closer to understanding the true potential and limitations of our method. The culmination of this initial journey, eventually published in 2010, was the rigorous statistical analysis of our observations, validating our approach and providing a concrete (pun intended!) foundation for future research.

Annamdas V. G. M ,Yang Y and Soh C. K.(2010) "Impedance based Concrete Monitoring using Embedded PZT Sensors" International Journal of Civil & Structural Engineering, Vol 1, Issue 3, PP: 414-424 (full paper)

This wasn't just a project; it was my initiation. It was the moment I learned that even the most "simple" ideas in research can hide layers of complexity, demanding creativity, persistence, and a willingness to embrace the unexpected. And it was, unequivocally, dramatic.

2004-05

The Invisible Watchman: My Second Act in Smart Materials

My second year as a PhD student. The initial thrill of discovery from my first project had settled into a focused determination. While surface-bonded piezoelectric ceramic (PZT) transducers were making waves in structural health monitoring, I was already looking ahead, delving deeper into the realm of the unseen. My new challenge: embedding PZT patches directly into sandwiched beams, creating an invisible watchman for structural integrity.

Beyond the Surface: The Quest for Durability

The limitations of surface-bonded sensors were becoming clear. Vulnerability to environmental wear, damage, and even vandalism—these were real concerns for long-term monitoring. My vision was to overcome this. Embedding the PZT offered the promise of durability and protection, shielding the delicate sensors from the harsh realities of their environment. This wasn't just about placing a sensor; it was about integrating it so seamlessly that it became an intrinsic part of the structure itself.

Unveiling the Unseen: Thickness Vibration and "Average Sum Impedance"

This project pushed me to think beyond the conventional. I aimed to utilize the thickness vibration of the PZT patch within the electromechanical admittance formulations. This was a crucial step, unlocking a new dimension of sensing. But the true breakthrough came with the development of a novel concept: 'average sum impedance'. This wasn't just a theoretical construct; it was the key to unlocking the hidden mechanical secrets of the host structure.

The beauty of this new model was its versatility. The formulations we developed could be effortlessly used to extract the mechanical impedance of any 'unknown' PZT patch embeddable plane structure. Imagine the power: from the simple electrical admittance signatures of an embedded PZT, we could deduce the mechanical health of the entire beam. It was like giving the structure its own voice, allowing it to communicate its internal state through subtle electrical whispers.

From Concept to Concrete: Experimental Validation

The ultimate test, as always, lay in the lab. We meticulously designed and conducted experiments on sandwiched beams to rigorously verify our proposed model. Each experiment was a high-stakes performance, a dramatic unveiling of whether our theoretical breakthroughs would hold true in the physical world. The successful experimental verification was a moment of profound satisfaction, confirming that our invisible watchmen were indeed capable of listening and interpreting the vital signs of the structures they protected.

This project wasn't just another research paper; it was a testament to the power of pushing boundaries, of daring to embed and to derive, and of transforming abstract concepts into tangible, powerful tools for the future of structural health monitoring. It solidified my path in smart materials, reinforcing the notion that true innovation often lies just beneath the surface.

Paper: Annamdas V. G. M and Soh C. K (2006) "Embedded piezoelectric ceramic transducers in sandwiched beams", Smart Materials and Structures, Volume 15, Issue 2: 538-549, (Link to Paper)

2005-06

The Grand Finale: Unleashing the Power of 3D Impedance

My final year as a PhD student was a crescendo, a culmination of everything I had learned and pioneered. Piezoceramic transducers (PZTs) were already well-established in vibration control and damage detection, but a critical gap persisted in the burgeoning field of electromechanical impedance models. These models, though promising, were largely limited to one- or two-dimensional extensional actuations of the transducer, effectively ignoring their crucial longitudinal vibrations. This, I realized, was the missing piece of the puzzle. My ambition for this final year: to develop a three-dimensional (3D) electromechanical impedance model.

Breaking the Dimensional Barrier: Unrestricted Sensing

This wasn't just an incremental improvement; it was a fundamental paradigm shift. My goal was to create a model that comprehensively captured the 3D interaction of a transducer with its host structure, accounting for both extensional and longitudinal actuations. Crucially, this new model was designed to impose no restrictions on the shape, size, or electrical properties of the PZT. This meant it possessed additional features and capabilities far beyond any existing PZT-structure interaction models. It was about truly understanding the PZT's full potential as a sensor, in all its vibrational glory.

This monumental effort was published in two distinct, yet interconnected, parts:

Annamdas V. G. M and Soh C. K (2007) "Three Dimensional Electromechanical Impedance Model I: Formulation of Directional Sum Impedance", Volume 20, Issue 1: 53-62, Journal of Aerospace Engineering, American society of Civil Engineers (ASCE).
Annamdas V. G. M and Soh C. K (2007) "Three Dimensional Electromechanical Impedance Model II: Damage analysis and PZT characterization", Volume 20, Issue 1: 63-71, Journal of Aerospace Engineering, ASCE.

Part I laid the theoretical groundwork, presenting a groundbreaking "directional sum" numerical–analytical admittance formulation, rigorously validated through experimental verification. Part II then delved into the practical applications, elaborating on damage analysis and the intricate characterization of PZT properties within this new 3D framework.

The Unseen Layer: Tackling Thick Adhesives

Real-world applications often present unforeseen complexities. One such challenge was the presence of thick adhesive bonding, a common reality in many structural components. To ensure the robustness and applicability of our 3D model, it was imperative to validate its performance under these conditions. This led to a focused investigation, the results of which were detailed in:

Madhav A. V. V. G and Soh C. K (2007) "Electromechanical Impedance Model of Piezoceramic Transducer - Structure in Presence of Thick Adhesive Bonding", Smart Materials and Structures, Volume 16, Issue 3: 673-686.

This paper underscored the model's resilience and adaptability, proving its efficacy even when faced with bonding layers that could otherwise distort critical sensor readings.

The Dynamic Challenge: Loading vs. Damage

As my PhD journey neared its end, another crucial real-world consideration emerged. While the electromechanical (EM) admittance signatures of PZT transducers (their real and imaginary parts) were powerful indicators of structural health, how did they behave under external loading, a constant in real-life structures like slabs, beams, and columns? This was a vital distinction to make: separating the influence of applied stress from actual damage.

This led to a compelling experimental and statistical investigation, revealing a subtle but significant truth: the EM admittance signatures obtained from a loaded structure were distinct from those indicative of damage. More profoundly, we observed that the susceptance signature was a superior indicator compared to the conductance signature for detecting in situ stress within the host structure. This pivotal finding, further bolstered by rigorous statistical analysis, held immense implications for the non-destructive evaluation of engineering structures under dynamic conditions. This critical insight was shared in:

Annamdas V. G. M, Yang Y and Soh C. K (2007) "Influence of loading on the electromechanical admittance of piezoceramic transducers", Smart Materials and Structures, Volume 16, Issue 5: 1888-1897.

This final year was an intense sprint, culminating in a suite of publications that not only advanced the fundamental understanding of PZT-structure interaction but also addressed critical practical challenges. It was the capstone of my PhD, a testament to the power of pushing boundaries, embracing complexity, and ensuring that theoretical breakthroughs could truly stand the test of real-world application.

Thesis

My Thesis: Characterizing Smart PZT Transducers for Structural Health Monitoring

My PhD thesis, "Characterization of Smart PZT Transducer and Admittance Signatures using PZT-Structure Interaction Models for Structural Health Monitoring," was the culmination of years of dedicated research, born from a critical need. In the wake of numerous catastrophic failures and damages to existing aerospace, civil, and mechanical (ACM) structures—whether due to natural calamities or the relentless wear and tear of continuous use—structural health monitoring (SHM) had transformed from a specialized field into a regular and vital practice. The last few years had witnessed an explosive growth in nondestructive evaluation (NDE) based SHM, primarily driven by the emergence of the electromechanical impedance (EMI) technique.

The Power of Electromechanical Impedance

The EMI technique, at its heart, employs piezoelectric-ceramic (PZT) transducers to predict a structure's response, which manifests as its electromechanical (EM) admittance. This response acts as a unique "signature" of the structure's health. My research aimed to refine and expand this technique, making it more robust and versatile for a wide array of engineering structures.

Tailoring PZT Application to Structural Stiffness

A key insight driving my thesis was the critical relationship between the PZT transducer and the stiffness of the host structure. I recognized that engineering structures could broadly be categorized into two groups: those stiffer than the PZT material and those less stiff. This distinction proved crucial for optimizing PZT application:

Surface-bonded PZT transducers are more effective when applied to structures that are stiffer than the PZT itself.
Embedded PZT transducers, conversely, excel when integrated into structures that are less stiff than the PZT.

Both types of PZT transducers are indispensable for EMI-based NDE across these two categories of engineering structures. While surface-bonded PZT transducers had seen more prominent applications in recent SHM efforts, my research provided a comprehensive framework that encompassed both.

A Comprehensive Approach: My Thesis Contribution

My thesis didn't just review existing methods; it actively developed both surface-bonded and embedded PZT-structure interaction models specifically for the SHM of both existing and future ACM structures. It was a holistic endeavor, bringing together the theoretical advancements and experimental validations from my previous work, and presenting them as a unified, powerful approach to structural health monitoring. This body of work laid the foundation for more accurate, durable, and versatile methods of ensuring the safety and longevity of our critical infrastructure.

Thesis Link

People (2003-06)

My Students: Mr. TIONG YEN-LUN (nick), Mr. CHIAN SIAU CHEN (Later became Professor in NUS Singapore)

Freelance Research Assistant (Dec 2005 - July 2006): Mrs. Radhika Madhav (Presently working in Birla Open Minds International School, Hyderabad, India)

Freelance Research Assistant (March 2004): Ms. Mitaly Srivastava (Later moved to Vienna, Austria)

My Supervisor: Prof. Soh Chee Kiong, Sch of CEE, Nanyang Technological University Singapore

Mentor (Aug 2003-Feb 04): Mr. Suresh Bhalla (Later he became Professor in IIT Delhi)

Mentor (Aug 2003- Feb 04) for emotional quotient: Mrs. Rupali Suresh

Some Pictures