A flexible piezoelectric thin-film ultrasonic sensor capable of broadband response and high linearity

Abstract Ultrasonic inspection plays a pivotal role in evaluating the insulation integrity of power equipment and monitoring structural health. Flexible piezoelectric acoustic sensors, capable of conforming to curved surfaces and operating reliably in complex electromagnetic environments, have therefore received increasing attention. In this work, a high-performance flexible 0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 (PMN-PT) piezoelectric thin-film ultrasonic sensor enabled by LaNiO 3 (LNO)/Mica was developed. Incorporating a conductive LNO buffer layer onto the mica substrate preserved mechanical flexibility while markedly enhanced the preferred crystal orientation of the PMN-PT film, thereby achieving well-defined ferroelectric hysteresis, low leakage currents and stable piezoelectric output. With the integration of a flexible encapsulation strategy, the fabricated PMN-PT sensor achieved an effective bandwidth of up to 600 kHz, an average sensitivity exceeding 60 dB, and a peak sensitivity of ∼80 dB. The ball-drop impact experiments based on Hertzian contact theory further revealed the linear relationship between the output voltage and the impact height h 0.2 ( R 2 > 0.98), confirming the excellent linearity and operational stability of the sensor. In summary, the flexible piezoelectric thin-film ultrasonic sensor offers significant potential for high-frequency acoustic emission detection, partial discharge monitoring, and next-generation flexible acoustic sensing technologies.