We study the feasibility and the repeatability of the electromechanical impedance (EMI) method for the health monitoring of lightweight bonded joints. The EMI technique exploits the coupling between the displacement field and the potential field of a piezoelectric material, by attaching or embedding a piezoelectric transducer to the structure to be monitored. The sensor is excited by an external voltage and the electrical admittance which is the ratio between the electric current and the applied voltage is measured as it depends on the mechanical coupling between the transducer and the host structure. Owing to this interaction, the admittance may represent a signature for the health of the host structure. In this study the EMI method is applied to aluminum joints adhesively bonded. We investigate the repeatability of the proposed method by monitoring the same aluminum components bonded many times using the same adhesive mix, and then by monitoring the same two components bonded several times by means of different adhesive qualities. The results demonstrate that the EMI is repeatable and variations in the admittance signatures are related to the quality (health) of the bond.
The achievement and the maintenance of dental implant stability are prerequisites for the long-term success of the
osseointegration process. Since implant stability occurs at different stages, it is clinically required to monitor an implant
over time, i.e. between the surgery and the placement of the artificial tooth. In this framework, non-invasive tests able to
assess the degree of osseointegration are necessary. In this paper, the electromechanical impedance (EMI) method is
proposed to monitor the stability of dental implants. A 3D finite element model of a piezoceramic transducer (PZT)
bonded to a dental implant placed into the bone was created, considering the presence of a bone-implant interface
subjected to Young’s modulus change. The numerical model was validated experimentally by testing bovine bone
samples. The EMI response of a PZT, bonded to the abutment screwed to implants inserted to the bone, was measured.
To simulate the osseointegration process a pulp canal sealer was used to secure the implant to the bone. It was found that
the PZT’s admittance is sensitive to the stiffness variation of the bone-implant interface. The results show that EMIbased
method is able (i) to evaluate the material properties around the implant, and (ii) to promote a novel non-invasive
monitoring of dental implant surgical procedure.
KEYWORDS: Ferroelectric materials, Electromagnetic coupling, Adhesives, Aluminum, Structural health monitoring, Transducers, Nondestructive evaluation, LabVIEW, Digital signal processing, Signal processing
The low weight, robustness and fatigue resistance of adhesive joints make them suitable for structural joints. A fully developed nondestructive evaluation technique however is needed to monitor and assess the quality of bonded joints. In the present paper the application of the electromechanical impedance (EMI) technique is proposed. In the EMI method a piezoelectric transducer (PZT) is attached to the structure of interest. The high sensitivity and low power consumption make the EMI method feasible for real time structural health monitoring. In this study we investigated the sensitivity of the electromechanical response of a PZT to the curing and the quality of the adhesive used for bonded joints. A PXI unit running under LabView and an auxiliary circuit were employed to measure the electric impedance of a PZT glued to an aluminum plate. The system aimed at monitoring the bond line between an aluminum strip and the plate. The conductive signature of the PZT was measured and analyzed during the curing. The experimental results show that the electromechanical impedance technique is sensitive to the curing time and variations are observed for adhesives of different quality.
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