Piezoelectric thin films have become increasingly significant in applications such as MEMS devices, wearable electronics, and lab-on-a-chip systems due to the miniaturization and integration of electronic devices. For piezoelectric thin films, even when an electric signal is applied in the thickness direction, greater deformation can often be observed in the in-plane direction, which is perpendicular to the electric field. Therefore, piezoelectric thin film devices are frequently designed using the transverse mode. As a result, it is crucial to evaluate piezoelectric thin films by measuring their transverse piezoelectric coefficient. This tutorial paper introduces a method for evaluating the effective transverse piezoelectric coefficient (e_31,f) of piezoelectric thin films using laser Doppler vibrometry (LDV). Additionally, the paper outlines a step-by-step procedure for measuring e31,f while using Bi_1/2Na_1/2TiO₃-based piezoelectric thin films as an example. This tutorial is expected to provide a practical and valuable method for measuring and analyzing the transverse piezoelectric properties, thereby supporting the development of new piezoelectric thin film materials.

Morphotropic phase boundary (MPB), which is a special boundary that separates two or multiple different phases in the phase diagram of some ferroelectric ceramics, is an important concept in identifying physics that includes piezoelectric responses. MPB, which had not been discovered in organic materials until recently, was discovered in poly(vinylidene fluoride-co- trifluoroethylene (P(VDF-TrFE)), resulting from a molecular approach. The piezoelectric coefficient of P(VDF-TrFE) in this MPB region was achieved up to -63.5 pC N^-1, which is about two times as large as the conventional value of -30 pC N^-1 of P(VDF-TrFE). An order-disorder arrangement greatly affects the rise of the piezoelectric effect and the ferroelectric, paraelectric and relaxor ferroelectric of P(VDF-TrFE), so the arrangement and shape of the polymer chain is important. In this review, we investigate the origin of negative longitudinal piezoelectric coefficients of piezoelectric polymers, which is definitely opposite to those of common piezoelectric ceramics. In addition to the mainly discussed issue about MPB behaviors of ferroelectric polymers, we also introduce the consideration about polymer chirality resulting in relaxor ferroelectric properties. When the physics of ferroelectric polymers is unveiled, we can improve the piezoelectric and pyroelectric properties of ferroelectric polymers and contribute to the development of next-generation sensor, energy, transducer and actuator applications.

Ultrasound imaging by using piezoelectric materials, such as lead zirconium titanate (PZT) has been oneof the most preferred modes of imaging in the medical field due to its simple, low cost and non-ionizing radiation in comparison to other imaging techniques. Recently, the market demand for portable ultrasound is becoming larger with applications in developing countries, disaster area, military, and emergency purposes. However, most of ultrasound probes used is bulky and high power consumable, so unsuitable for such applications. In this study, the 3 layered ceramic specimen consisted of 128 pitches of 420 μm in width and 450 μm in thickness were prepared by using the Ti-rich PZT compositions co-fired at 1,050℃. Their electrical and ultrasound pulse-echo properties were investigated and compared to the single layer specimen. The 3 layered ultrasound probe showed 1.584 V of Vp-p, which is 3.2 times higher than single layered one, implying that it would allow effectively such a portable ultrasound probe system. The result were discussed in terms of higher capacitance, lower impedance and higher dielectric coefficient of the 3 layered ultrasound probe.