On a Highly Reproducible, Broadband Nanocomposite Ultrasonic Film Sensor Fabricated by Ultrasonic Atomization‐Assisted Spray Coating

Owing to their physical flexibilities and high sensitivities to dynamic strains, nanocomposite film sensors are explored extensively to achieve condition monitoring of engineering structures. However, the existing nanocomposite sensors for acquiring ultrasonic waves struggle to attain wide applications due to their notably low reproducibility and consequent poor stabilities in sensitivity. Herein, a highly reproducible carbon black/polyvinylpyrrolidone nanocomposite ultrasonic sensor is fabricated by ultrasonic atomization-assisted spray coating. To maximize sensitivity and stability, the spraying ink is carefully designed, and the spray coating process is systematically optimized, resulting in a precisely controlled fabrication process, which warrants a high uniformity in the coalescence of sensor films and in the establishment of quantum tunneling networks inside sensors. Benefitted from an even distribution of quantum tunneling paths, the piezoresistive nanostructure of the proposed sensor exhibits an exceptional sensitivity to ultrasonic waves over a broad frequency bandwidth of up to 500 kHz. Also, both the sensitivity and the stability of the proposed sensor outperform those of sensors that are fabricated by other reported forming techniques. The superior reproducibility of the sensor is crucial to promoting it to real-world applications.