investigating-potential-singly-curved-thin-piezoelectric-transducers

Investigating the Potential of Singly Curved Thin Piezoelectric Transducers for Energy Harvesting and Structural Health Monitoring

Over the past two decades, piezoelectric materials have become an integral part of structural health monitoring (SHM) and energy harvesting. These ...

Indian Institute of Technology Delhi

Directly bonded piezo sensor, conventionally employed in the electromechanical impedance (EMI) technique, although a proven candidate for structural health monitoring, is severely constrained in its application in the biomedical field due to its bonding requirement. In contrast, nonbonded piezo sensor (NBPS) provides a viable platform to assess the condition of human bones, tissues, and other biomedical subjects using the EMI technique without inflicting pain or irritation to the skin. The name NBPS was coined to emphasize that there was no direct bonding between the PZT patch and the live subject; instead, the PZT patch was bonded to a supporting medium, which maintains the mechanical interaction between the PZT patch and the subject. However, there are several aspects in the analysis of NBPS configuration that cannot be addressed completely through experimental study due to measurement constraints, cost, and time. For example, experimentally changing the density of bone continuously to study the osteoporosis effect is a tedious task warranting large number of specimens. This paper presents a detailed parametric study based on finite element method covering condition monitoring of human bones using the NBPS configuration. It is for the first time that 3D analysis for specimen identification and damage detection in bones using NBPS has been carried out. In addition to the validation of the numerical model against the previously established experimental studies involving bones, quantification of the extent of damage and its localization has been investigated. The density changes due to osteoporosis in bones are comprehensively investigated by the NBPS including the quantification aspect of osteoporosis/damage. Definite acquisition of bone signature and detection of physiological changes in bones are achieved even with the presence of skin, muscle, and fat layers on the bone.

Numerical evaluation of nonbonded piezo sensor for biomedical diagnostics using electromechanical impedance technique.

In the recent years, there has been a growing interest in research community towards the application of smart materials for bio-medical structural health monitoring. Amongst the smart materials, directly bonded piezo sensors (DBPS), based on the electro-mechanical impedance (EMI) technique, have been successfully employed for the above purpose. The principle behind the EMI technique is that high frequency excitations (typically > 30 kHz) generated by a surface bonded PZT patch are used to detect changes in structural drive point impedance caused by cracks or any other type of damage. Bone healing and damage have been shown to be successfully monitored using the DBPS. However, in most of the diagnostic cases of live human and animal subjects, directly bonding a PZT patch is always an irritant or hazard for a live subject. To circumvent direct bonding, the authors have developed and experimentally demonstrated a non-bonded piezo sensor (NBPS) configuration as a good alternative to DBPS while maintaining the effectiveness of measurement well within discernible limits. This paper presents further improvement in the NBPS configuration aiming at autonomous operation of the gripping mechanism using shape memory alloy (SMA) wires. The experiments are performed on replicas of femur bone in healthy and osteoporosis state. This paper shows the effective use of SMA clamping for bone identification and its damage assessment in comparison to earlier mechanical gripping using jubilee clamps. This paper also covers impedance based identification applied to SMA and clamp based NBPS configurations. In place of raw admittance signatures, effective drive point impedance is utilized for the purpose of bone diagnostics which provides a more realistic assessment of the condition of bone.

Shape memory alloy actuation of non-bonded piezo sensor configuration for bone diagnosis and impedance based analysis.

Electro-mechanical impedance (EMI) and the vibration-based monitoring techniques deploy piezoelectric sensors that are permanently bonded to the structural surface. This increases the risk of sensor degradation over time and raises monitoring costs due to the need for multiple sensors. This study explores the development and performance of reusable single magnet-bonded piezoelectric sensor (MBPS) for damage monitoring in steel structures to address these limitations. In this study, MBPS is evaluated for capturing bolt looseness by measuring root mean square deviation (RMSD) using the EMI technique and curvature change during modal testing. The MBPS configuration demonstrates high repeatability (Correlation Coefficient > 99.5%), ensuring reliability for SHM applications. Piezo disc buzzer MBPS, noted for having the highest sensor-to-magnetic base area ratio, displays the highest RMSD index in the miniature specimen. It also effectively identifies damage in a thin-walled steel plate using the RMSD damage index (RDI) and the curvature damage index (CDI) across multiple damage states. The damage indices are found to be highest at the actual damage locations but are at the same time significantly spread over the adjacent undamaged panels, exhibiting an umbrella-like formation. A novel hybrid damage index (HDI) is proposed that fuses the local and the global monitoring techniques, integrating higher-order RDI and CDI, thereby effectively reducing noise over the undamaged panels adjacent to the damaged ones. MBPS paired with HDI offers a highly effective and robust monitoring solution as an alternative to bonded piezoelectric sensors, providing a blend of high sensitivity, flexibility, and resilient damage monitoring for various SHM applications in steel structures.

Article	Year
Numerical evaluation of nonbonded piezo sensor for biomedical diagnostics using electromechanical impedance technique. International journal for numerical methods in biomedical engineering\| PubMed ID: 30281937	2019
Shape memory alloy actuation of non-bonded piezo sensor configuration for bone diagnosis and impedance based analysis. Biomedical engineering letters\| PubMed ID: 31799013	2019
A novel integrated framework for damage detection in steel structures using magnetic piezoelectric sensors and hybrid damage index. Scientific reports\| PubMed ID: 41093971	2025

Suresh Bhalla

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