Lead-free KNN-based Ultrasonic transducer for wide-temperature imaging applications

In recent years, eco-friendly lead-free KNN-based piezoelectric materials, which exhibit exceptional thermal stability, have garnered extensive attention and have witnessed substantial advancements. To further enhance their applicability, wide-temperature ultrasonic transducers based on lithium-modified KNN (KNLN) ceramics have been developed. These transducers were meticulously designed and fabricated to operate effectively across a broad temperature range. Key material properties, including the thickness-direction electromechanical coupling coefficient, acoustic impedance, sound velocity, and dielectric constant, were thoroughly characterized from 25 °C to 200 °C to guide the design and simulation process. The performance of KNLN ultrasonic transducers demonstrated remarkable thermal stability comparable to lead-based devices. Moreover, the ultrasonic imaging capabilities of the transducers were validated between 25 °C and 200 °C through the acquisition of images for a standard non-destructive testing block. This study marks the first successful deployment of KNN-based transducers at temperatures up to 200 °C, highlighting the potential of KNLN ceramics for wide-temperature applications.