Measurement of defects in a plate using dry-coupled interdigital transducer–based scanning laser Doppler vibrometer

The interdigital transducer–based scanning laser Doppler vibrometer has recently been introduced to efficiently generate the symmetric mode for damage detection of shallow defects in thick plates. To measure shallow defects in a carbon steel plate, the excitation frequency is optimized based on the analysis of wavenumber sensitivity and degree of separation between modes. Even though the interdigital transducer–based scanning laser Doppler vibrometer method using continuous excitation is a promising method for visualizing defects in plate-like structures, the interdigital transducer has to be coupled to media, such as oil or water, to minimize the variation in acoustic impedance between the lead zirconium titanate and the plate-like structures. In this study, we develop a dry-coupled interdigital transducer–based scanning laser Doppler vibrometer system for the detection of shallow defects in a plate to facilitate easy mounting and demounting from the plate. To verify the proposed dry-coupled interdigital transducer–based scanning laser Doppler vibrometer, plates with four and eight different depth defects are introduced, and it is demonstrated that the defects in thick plates measured by dry-coupled interdigital transducer–based scanning laser Doppler vibrometer are visualized compared to those measured by interdigital transducer–based scanning laser Doppler vibrometer.

Fabrication of Piezoelectric Composites Using High-Temperature Dielectrophoresis

In this paper, we present a method to create a highly sensitive piezoelectric quasi 1–3 composite using a thermoplastic material filled with a piezoelectric powder. An up-scalable high-temperature dielectrophoresis (DEP) process is used to manufacture the quasi 1–3 piezoelectric polymer-ceramic composites. For this work, thermoplastic cyclic butylene terephthalate (CBT) is used as a polymer matrix and PZT (lead zirconium titanate) ceramic powder is chosen as the piezoelectric active filler material. At high temperatures, the polymer is melted to provide a liquid medium to align the piezoelectric particles using the DEP process inside the molten matrix. The resulting distribution of aligned particles is frozen upon cooling the composite down to room temperature in as little as 10 min. A maximum piezoelectric voltage sensitivity (g33) value of 54 ± 4 mV·m/N is reported for the composite with 10 vol% PZT, which is twice the value calculated for PZT based ceramics.