2008-2009

Transcontinental Guidance: Pioneering Parallel Interrogation from Afar

My move to the USA for a postdoctoral position marked a new phase in my career, but my connection to the cutting edge of structural health monitoring in Singapore remained strong. Even as I embarked on new research in the States, I continued to remotely guide students back in Singapore, extending my expertise across continents. This unique setup allowed us to push the boundaries of PZT-based SHM, culminating in groundbreaking work on parallel interrogation of piezoceramic transducers.

The Challenge of Location: Beyond Single Sensor Detection

In recent years, lead zirconate titanate (PZT)-based piezo-impedance transducers had proven their worth in SHM. A single PZT, while remarkably sensitive to the presence of damage, fell short when it came to the crucial task of identifying the damage location. This limitation was a significant hurdle in practical applications. If we could pinpoint where damage occurred, we could enable more efficient and targeted repairs. This became the driving force behind the work I guided from the USA.

Unlocking Location: The Power of Parallel Interrogation

To tackle this challenge, our team in Singapore embarked on an innovative study. We strategically surface-bonded nine PZT transducers onto an aluminum plate. The core idea was to explore the feasibility of precisely locating induced damages. At each simulated damage state, we meticulously recorded the electromechanical admittance signatures from all PZT sensors. The Root Mean Square Deviation (RMSD) index—a powerful tool for quantifying changes in these signatures—was then employed to analyze the results.

The findings were significant: the damage location could indeed be estimated by analyzing the RMSD patterns. Crucially, this was achievable through both parallel and individual interrogations of the PZTs.

The advantage of parallel interrogation over single interrogation is profound. A single PZT can tell you if something is wrong within its sensing range. However, by simultaneously interrogating multiple PZTs, and analyzing their combined RMSD responses, we create a "fingerprint" of the damage. When damage occurs, the RMSD values of the PZTs closest to the damage will show a more pronounced change than those further away, creating a discernible pattern that directly correlates to the damage's spatial position. This ability to localize damage significantly enhances the efficiency and effectiveness of structural maintenance and repair.

This pivotal work was published in:

• Yang Y, Liu H and Annamdas V. G. M (2010) "Parallel Interrogation of Piezoceramic Transducers in Electromechanical Impedance Technique for Quick Damage Detection", Materials and Manufacturing Processes, Volume 25, Issue 4: 249-254.

The principles we elucidated in this study also formed the basis for further contributions, including a book:

• Hui L , Yang Y and Annamdas V. G. M (2011) "Identification of Structural Damage Location Using Impedance Sensors", Publisher: LAP- Lambert Academic Publishing, Germany, Dec- 2011. ISBN: 978-3-8465-9362- 2.

Knowledge Across Borders: Impact in the USA

While the published work on parallel interrogation was conducted in Singapore, the deep understanding and methodologies I developed found immediate application in my new role in the USA. My expertise in SHM, particularly with smart sensors and impedance techniques, was directly utilized in a significant project for PennDOT (Pennsylvania Department of Transportation). This was a direct extension of my prior research, translating the theoretical and experimental successes from Singapore into practical solutions for critical infrastructure in the United States. My knowledge, forged in the diverse environments of my PhD and initial post-doc, was now making a tangible impact on a global scale.