Study of advanced integrated piezoelectric sensor systems for the evaluation of structures and materials

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Developing compact, sensitive, durable, inexpensive real-time sensors for mechanical measurements represents a significant engineering challenge and has received considerable attention from research and industrial communities. Among the commonly used sensors, piezoelectric sensors are often the most attractive, which offer the highest power density and the relative ease of application. Their high electromechanical coupling and almost instantaneous response time enable the effective conversion of mechanical measurements into electric signals with a relatively high sensitivity and high resolution. Piezoelectric sensors are currently used in various engineering applications, such as the nondestructive evaluation of structures to detect cracks and damage, the characterization of the mechanical property of thin films to determine their thickness and modulus, and the chemical and biological surface-acoustic-wave devices to identify chemical and biological species, to name a few.**Major impediments to the wider application of piezoelectric sensors are (i) the limitation by their minimum detectable stress, and (ii) the difficulty in integrating signals from multiple sensors. Existing techniques based on individual piezoelectric sensors can only be used in situations where a very limited number of parameters need to be determined. This results in major difficulties in quantitative nondestructive evaluation of structures containing embedded damage and in the detection of multiple chemical and biological species in surface-acoustic-wave devices.**It is, therefore, the objective of the current project to study highly sensitive integrated piezoelectric sensors and develop an imaging technique for the quantitative evaluation of structural integrity. To develop highly sensitive sensors, study of metamaterial-based piezoelectric sensors will be conducted. Metamaterials refer to new types of composites exhibiting exceptional properties not commonly observed. The new piezoelectric sensors will be composites containing carefully designed local structures, from which high sensitivity can be achieved through the internal interaction between them. For damage imaging, by integrating signals from multiple piezoelectric sensors, the wave propagation near the sensors can be regenerated and studied. An inverse process based on the signals from the multiple sensors will then be established to quantitatively identify the anomalies, which have disturbed the wave propagation. **Both theoretical and experimental studies will be conducted. The main steps of the research include: (i) Developing a unified and fundamental dynamic model of interacting piezoelectric elements, in forms of fibres and sheets, under different loading and boundary conditions, (ii) Using the developed model to evaluate the behaviour of new piezoelectric sensors with designed local structures, which form interacting piezoelectric elements, and study the relation between the sensitivity of the sensors and the arrangements of the local structures, (iii) Studying sensor response to different embedded anomalies, and developing an inverse technique to quantitatively identify embedded defects, (iv) Conducting experimental studies for verifying the theoretical predictions, evaluating new sensor designs and studying integrated multiple sensors for quantitative imaging of damage.**The proposed study will significantly improve the understanding and provide important knowledge for the design of piezoelectric sensors. The project also represents a new topic in nondestructive evaluation and other related areas. Its feasibility has been clearly shown from our recent research results. In the long term, the outcome of the research can be used in the design of next generation piezoelectric sensors.