TOWARDS META-FIXTURE DESIGN FOR INDIRECT ELECTROMECHANICAL IMPEDANCE MEASUREMENTS: ON THE EFFECTS OF ELASTIC METASTRUCTURES ON DEFECT DETECTION CAPABILITIES

Electromechanical impedance (EMI) measurements have seen an increased application in the assessment of the structural integrity of manufactured parts. This has allowed for a costeffective and simple solution to non-destructively evaluate additively manufactured components. EMI-based nondestructive evaluation (NDE) is normally conducted by instrumenting individual parts with piezoelectric wafers. Recently, indirect EMI measurements have been proposed as a rapid NDE solution for manufactured parts. With indirect EMI, manufactured parts are inspected through an instrumented fixture, which alleviates the need for individual part instrumentation, reducing measurement cost and time. EMI signatures obtained for the fixture-part combination are found to be dominated by the fixture's dynamic response. It is hypothesized that integrating the concepts of elastic metastructures in the fixture design allows for obtaining EMI signatures that are dominated by the part itself, leading to an improved defect detection capability. This paper investigates the effects of elastic metastructures on EMI signatures and defect-detection capabilities. For this purpose, a set of beams with integrated mechanical resonators are designed and fabricated. Frequency response functions of the beams are then experimentally measured to identify the bandgaps. The EMI signatures of the beam are measured over the frequency range encompassing the beam's bandgap. This is then compared with the signature obtained when structural changes at the opposing beam end are introduced. The sensitivity of EMI signatures measured over these frequency ranges is then evaluated to assess the impact of bandgap on defect detection capabilities. This work is a first step in investigating the feasibility of eliminating the fixture's dynamics from the measured EMI signature for indirect EMI-based NDE.